Very little. I like Fallout's system the best. You set your SPECIAL at the start and then you can only permanently increase some by finding rare implants or any of them by spending a very valuable trait which you obtain after each 3 or 4th level.
I find the system far more believable than other RPGs like Diablo or Morrowind where you start with 10 strength and end with 100.

There can also be an alternative option which is item/gear based like in the Dark Souls series.

In that kind of configuration, even if you can level up almost indefinitely (good luck reaching the hard cap...), in a normal playthrough, your progression will be mostly gear/item based depending on the stuff you find and how you upgrade it (knowing that you can only get 2-3 maxxed up gears per new game). It's a kind of good in-between solution as you aren't stuck into endless XP farming but can rather aim at gear/upgrade hunting if you don't have much free time to play. It's a much more flexible solution for different players.

You get The Secret World, more or less.

There are no stats in the traditional sense, you get ability points which are then spent towards acquiring various skills on the ability wheel. Skills farther out on the wheel cost more and have skills nearer the center as prerequisites, but there are no classes. It's intended for you to eventually be able to learn every ability in the game. Bonuses primarily come from equipment, and you gain access to better equipment as you progress.

It's one of two MMOs I've ever enjoyed playing, due to the heavy story focus (and that story is one heck of a wild ride) and the flexibility to change your skills to suit the situation. (Plus it's "buy once, play forever", pay monthly for some perks if you want them, which is a subscription model I can support.)

I prefer slow but meaningful progression and having to deal with what you have.

All character advancement systems have classes and levels. If there's no advancement, then stats are blatantly pointless because there's no uncertainly anymore: I either have a stat satisfying a condition or not for the full duration of the game.

I think how much stat growth is acceptable all depends on the mechanics and pacing of the game.

I felt the stat growth in Grim Dawn was really good. Leveling was neither a chore or too easy and when did you level up, you got 3 points (when you're below level 50) and 1 stat point. Those points spent did make a difference....

...Unlike older versions of Diablo 2 where you leveled up a lot in Act 1, considerably less in Act 2 and ONLY ONCE in Act 3. Act 3 was a slog cos I never felt my character was making progress....

...and on the opposite end, we have Morrowind where it was too easy to level too fast. I went from a weaking to fairly powerful in just a few hours of gameplay. I never exploited any bugs either.
It's the same in the Gothic series but unlike Diablo and Morrowind, the pacing was much MUCH better :P

I'm more DND or use-based like Morrowind or quest for glory.

I really hate the "I killed a few skeletons now I have nuclear fusion powers in my fingers" sort of growth unless there is a story-based reason for it.

I like slow growth with pivotal moments of growth. That way, you get used to your character and then experience something new.

Wow. That actually might explain quite a bit.

It's clearly true. I haven't played SaGa so I can only speculate but here's the rough outline of a "classless" math engine.

Suppose you have five identical starting characters, 10 in every stat. You have 5 weapons -- sword, bow, fire spellbook, frost spellbook, staff -- that allow them to (better) perform associated actions: melee fighting, ranged fighting, casting fire spells, casting frost spells, healing+debuffing otherwise exremely dangerous undead and demons. Doing more of X makes a character better at X.

Suppose there is advancement and a finite amount of monsters to kill. Then you only have this much XP to distribute between skills / stats / characteristics / whatever, and every secondary attack irreversibly penalizes the main attack. Giving a fire mage a sword midgame to have her figure out which end is for business is't just bad, it might be straight-up impossible because you're in a battle with opponents with attack and defense in the vicinity of 100, and going in with 10 is simply going to lose you this particular battle.

If there's an infinite amount of monsters to kill (and perhaps a skill ceiling, or maybe you just want 1048577 in every stat so you write a shell script and leave the game playing itself as a screensaver on a second monitor), then the initial classplosion will be followed by a Big Crunch. It doesn't mean the classes don't exist.
(Developers usually think different classes are more fun so the ceiling doesn't get hit.)

Okay but suppose Fire has a Flaming Arrows spell which creates explosive projectiles with to-hit running off Archery and damage running off Fire Magic and it makes sense for a character to uselessly plink at low-level monsters for a while so she can shoot fusion bombs and be awesome later? Then it's another class, for a total of six: Warrior, Rogue, Fire Wizard, Frost Wizard, Hierophant and Nuclear Scientist.

We try the same thing with Frost Mage and find out that while slowing monsters and kiting them looks good on paper, it turns out the Warrior can't contribute because she's either getting hit as hard by a slow monster as by a fast one or does nothing on her turns, and Fire Mage can't contribute because fire removes the slow debuff, so frost archer ends up not being a thing.

It's 2017 and there are only 2 types of characters: with classes, and those that suck. And we really can't have characters that suck while better games are being sold at 90% off, and especially not in a game with xp ticks.

I mostly prefer slower leveling where you have to work quite a bit before you grow all powerful, or very static stats that make you work with what you have and make very little improvement.

I have far more experience with tabletop rpg games than I do with video game ones however.

If you fix fading suns up a bit so that new characters aren't very sucky at their secondary skills it's quite nice with characters only accumulating power and powerful technologies slowly. (unless you feed them incompetent grunts with fusion blasters and exosuits).

I remember World of Darkness, vampire the masquerade had a nice level curve, but that was long ago.

I generally think D&D is a bit quick with leveling. Especially in the early stages when the players still have to work hard to get their act together. As for D&D video games, I never played one (heresy, I know).

As for the elder scrolls; I don't exactly like their approach. I can't quite put my finger on it.

Glad to hear it. It's a series I want to check out one day. Somehow I completely missed it.

I'm not sure what I consider the best. I recall enjoying the level-up system in e.g. Icewind Dale. Except... did I have to re-roll to get good stats in the beginning? That I disliked a lot, I would have preferred it let me set the stats manually from a pool of points, without rerolling.

One thing I didn't like about the Fallout system was that later in the game it had things that made you go like "if I had known that in the beginning, I would have done this and this differently...". Not necessarily anything earth shattering, but might annoy you anyway.

Like if you invested a lot on strength... only to realize much later that e.g. power armors will bump your strength quite a lot. Or, at least in Fallout Tactics, there is also a perk which allows you to use much bigger weapons than what your current strength indicates so you don't necessarily even need a STR 9 to wield the most bad ass weapons. It is enough to have STR 5, then later bump it to 6 with a perk, and then e.g. use that perk that adds +3 when checking the strength requirements for a weapon. There, you can now use 9 STR heavy weapons without wasting the points on strength in the beginning.

Or, if you had even Charisma, e.g. 6... then when you get to bump it to 7 with a perk, it doesn't let you recruit any more party members than before because only the even Charisma numbers count there.

I just don't like the feeling I made some bad decisions in the beginning for which I can't do anything later on.

This is actually one reason I prefer bigger stat growth over the course of the game, so that mistakes made during character creation don't hurt you later in the game.

I also don't really like hard requirements, like the need to have X STR to equip heavy weapons, unless the game is set up so that a character who starts with minimum STR isn't stuck with having it low permanently. Games based on D&D 3.X have a similar issue with spellcasting stats; a character in a spellcasting class with a low casting stat is essentially worthless, and you don't get enough stat points during the game to have that character have any chance of being useful. Such requirements aren't so bad if you can significantly increase your stats, including those that start low, during the course of the game.

This sort of thing is also one reason I don't like skill point systems.

Oh yeah, but I think that is something that is difficult to avoid in rpgs in general? Not all weapons, spells or whatever are equally useful overall or just for your playstyle, so in that sense with the benefit of hindsight skill/stat points are usually wasted/misplaced to some extent.
But yes there are definitely a couple of things like that you should preferably know beforehand, like the minimum strength required to wield certain weapons, how charisma affects party size and how agility determines the number of action points. I didn't know any of it beforehand and only read up on in online as I continued playing, so I don't know to what extent the manual actually explains these things. I think I should in any case have read the manual beforehand though, at least to see what kind of perks there were. Specifically what the prerequisites were for some, like the insanely op sniper perk which has a high perception requirement and which, combined with decent luck, is absolutely lethal.
But at least in the first fallout it would be difficult to severely handicap your character without knowing any of these things. You can finish the game as a melee beast, a gunslinger or a smooth talker.