Okay, this is kind of a bad question, because I also posted a thread about Planescape Torment vs Icewind Dale vs Baldur's Gate, but I made the decision that I'd buy the other two after I got Baldurs Gate enhanced edition.

Now, onto the question, I want to get one of these two games (never played them before) but I don't know which one I should choose.

Thanks for answers!

Arcanum, while very good, is quite noticeably unfinished. It is a much more flawed game than Fallout, so if you're picking which one to play first... Pick Fallout.

Fallout has a great story but really lacks polish. Fallout 2 is much more refined. Also make sure you download killap's restoration project, the least it does is fix a lot of bugs. Whether you install the 'restored' content or not is up to you.
Arcanum is more like a sandbox. It's not 'balanced' but it need not be. It's just a very, very fun RPG.

Personally:
Fallout 2 > Arcanum > Fallout

I've never played Arcanum, so i don't know if it's good or not... but Fallout is in my top 10 best games of all time...

I mean, other than getting both (well, maybe three since you should get Fallout 2 as well...), I think it really depends on what kind of story/setting you like.

As Fenixp points out, Fallout (the first one particularly) feels much more "finished" than Arcanum does. Though with the game all patched up I don't really notice anything too bad in terms of bugs, or unfinished quests or such. There are some for sure, but it is a very long, and open game and so they are less galling (to me) than might be expected.

Other than that, as I said, I think the decision should really rest on if you like the idea of post-Apocalypse world (a la Fallout) and those ramifications (all while set in a technological mode around the 1950s or 1960s), or if you like the idea of a steampunk/magic fantasy setting (a la Arcanum) with those cliches, tropes, and other baggage.

I like Arcanum more. I bought it when it first came out and have played it gone back to it again and again over the past 10-11 years. It is that good to me. Fallout I only acquired a couple of years ago (through GOG) and while I love, didn't hit me in the same way that Arcanum did.

FALLOUT.

Hard one to decide, actually. While I would prefer Fallout on every other day, arcanum has a very interesting setting and the core game mechanic is so crazy that it actually worked - that is, that you can play as a machinist and make all sorts of contraptions and bombs and whatnot, but at the same time you get a severe penalty at using magic items. The explanation given, that both magicka and technology negate each other out and if a person has a certain aptitude towards one, the other will inevitably destroy itself around him. You can play as you like, and there is a good chance that whatever combination you choose to play will be good enough to finish the game.
In the end, you have to ask yourself if you like the post-apocalyptic setting or would you rather go for a full on fantasy-steampunk mash up.

I found FO2 to be substantially LESS polished than FO1. There's a lot more cut content and half-finished zones, there's several hundred more bugs, etc. Broken Hills and San Francisco don't have ANY items in ANY containers in the entire zones, except for plot-relevant stuff, for instance. It's a much bigger game and there's a lot more options available for practically everything, but polish it does not have.

Arcanum is a fun game, and it's got an interesting story much like Fallout does, but from a gameplay perspective it's got major issues. It's buggier even than FO2, several of the mechanics are just borked, (like item damage, grenades, or armor sizes) the party AI is even worse than in FO2 (though it's better than FO1 due to the interface) and magic characters are just obscenely powerful compared to tech characters. It's still a brilliant game, but those things impede my ability to enjoy it somewhat. However, I know plenty of folks who like it more than Fallout simply due to the setting, and you might be one of them. But for me, it comes behind FO and FO2... but it shouldn't feel bad, they're in my top 10 games of all time.

Both are very good, but I'd probably go with Fallout.

Arcanum pros:
-Interesting story (until about half-way)
-Very interesting setting (steam machines in a world of magic)
-Really good music
-Interesting ways to develop your character

Arcanum cons:
-Combat is quite dull, it's too fast even on turn-based and it looks like everyone's just swinging their swords/etc until the person in front of them dies
-Random encounters are often ridiculously hard when you're still a low-level character - you might run into a pack of level 25 were-rats when you're still starting out. And then you need to load your save.
-This is my opinion only, but I think the story loses a bit of its charm after half-way / during last third or fourth of the game.
-A diplomat character might have a hard time
-Random bugs here and there.

Fallout pros:
-Very interesting world
-Interesting story
-Good customization via perks (though Arcanum's is even better)
-Tons of guns and other weapons for you to find
-Satisfying combat

Fallout cons:
-To me, the game seems a little linear although you're free to travel anywhere
-Although the post-nuclear setting in itself is really interesting, the locations here are bit empty and monotone, in my opinion. Fallout 2 improved this (among everything else) a lot.
-Not many sidequests when you think about it, I mean they are there, but for an RPG you'd expect maybe a bit more. And no quests means no xp, so you might not see level ups as often as you'd expect.
-Follower interaction is needlessly complex (you need to buy your followers stuff, if you want to get rid of his useless items, whereas in Fallout 2 you can just take them)

Fallout 2 improved on Fallout in every level; better story, better (and longer) sidequests, better locales, even more weapons, some humor - everything. I recommend that game even more than Fallout or Arcanum, since you also don't really need to play Fallout to enjoy Fallout 2, but of course it's your choice. But you really can't go wrong with picking any of the mentioned titles, all three are really good games and among my favorites.

Mind you, I've only played FO about 2 or 3 times, in comparison to my at least 50 playthroughs of FO2 (not exaggerating).

I agree that FO2 can be a bit empty - especially towards the end, but killap's patch restores a lot of that and to be honest, empty containers never bothered me so much. Especially at the end you already have so much of everything, so why worry?

Fallout 2 has a story that you can finish at your own pace (in 10min from beginning to end if you wish) and a ton of sidequests to enjoy. That's what I felt was weak in FO, first of all the timer in the beginning and second of all the lack of sidequests.

It felt to me that many settlements which ought to have been rich with content were really just placeholders. Nobody would talk to you and people would have very little to say in general. I almost felt like I was on rails, with little to do besides the main quest.

Oh and don't worry about the bugs in FO2, fan patches fix literally thousands. Patched FO2 probably runs cleaner than your average modern AAA RPG.

I say flip a coin, heads = fallout, tails = Arcanum

You really can't go wrong either way. I love them both. They are similar in many ways yet so different you can't really compare them.

I haven't played both although I have been meaning to. I do not have Arcanum (well I did but lost the CD before I even had a chance to properly play it, so I do not have a copy right now). I have Fallout, so there's no excuse for not playing this yet except for the schedule.

I'd say though since quite a number of people seem to indicate that Fallout is not a long game that you give it a try first, maybe finish it quickly, and then move on to Arcanum.

One of these days I will also give Fallout a try. One of these days... *sigh*

Arcanum.

- Actually epic, multi-layered story, mindscrewy but in a good way. Ye olde "Bad guy wants to destroy the world" is not quite the same once the industrial revolution rolls around.
- Multiple plot lines, multiple quest solutions. For example, a basic "kill some bandits to get out of town" quest has 8.5 possible solutions.
- Many NPCs with their stories and quirks.
- Crafting items is tons of fun.
- Many viable characters and playstyles. Kill everyone and take their stuff? Why, sure. Sneak around and steal everything that isn't nailed down? Okay. Ask nicely? But of course!
- final argument supplied via PM

Fair warning:
- the final official version is buggy, use the Unofficial Patch (GOG post here).
- real-time combat sucks (turn-based is fine).

Both great games with unique settings. Fallout is better, more finished and entertaining in my opinion. Get both eventually, start with Fallout.