guess, you'll get lots of opposite opinions depending on the personal preferences of replying goglodytes.

yes!

I think most will say Morrowind, but Oblivion is more straight forward I think.
If you like THAC0 as opposed to literally hitting an enemy, then Morrowind. Also aliens.

Oblivion has made many very strange gameplay decisions.
Starting with the tile based structure for the landscape and for dungeons, so you see a lot very "familiar" dungeons, moving on to the enemies matched to your level all the time (including bandits wearing exceptional rare glass or deadra armor all the time to match you) to a character system you want to "game" it by not leveling your main professions to gain the best possible level up progress.

Morrowind tells the better story, but got a more strange environment. And I would call its game systems better.

Morrowind is more read and search, Oblivion is more hack and slash. Follow your desire!

One other interesting difference between these two games:
* In Morrowind, the game prefers not to limit the player. For example, early on you can find a consumable that briefly raises one of your skills by 1,000 points (when the normal limit is 100). Furthermore, if you find what looks like a possible way to exploit the game mechanics, Morrowind will probably let you, without providing any resistance.
* In Oblivion, if you try to exploit the game, the game will put up a lot of resistance; the game has mechanics to prevent the player from exploiting it too much (though they didn't catch all the exploits). Sometimes this comes at a cost; fortifying a skill above 100 won't usually provide a benefit, and Fortify Alchemy doesn't actually do anything except increase a number on your character sheet, for example.

I enjoyed Morrowind's lore and overworld more than Oblivion's, but Oblivion's combat is better than Morrowind's (although it is by no means perfect), also, Oblivion has some very well done side quests, somewhat better designed dungeons (though some designs get repetitive). Consider which things matter more to you. Both are good games so there is no bad choice here.

They both have their pluses. Be aware that as with any Bethesda game, you will need to add loads of mods to actually play them. For morrowind there is openmw, a modern engine for Morrowind with loads of good stuff. And I would suggest overhaul and rebirth.
https://openmw.org/en/
https://www.moddb.com/mods/morrowind-rebirth

For oblivion, you will at least a levelling mod as the levelling in vanilla is utterly pointless. I would follow a mod list such as bevelix:
https://www.nexusmods.com/oblivion/mods/47591

Get Skyrim.

If you have no nostalgia for either one, Morrowind's probably the better pick. Oblivion is decent and fun to dick around in, but it does run into that wall where it becomes an insidious origin story of where a lot of Bethesda's bad habits come from.

The Elder Scrolls Online has modern Morrowind content, if that's also a possibility.

The Elder Scrolls IV - OblIVion, obviously.

Morrowind is as bad as it gets. Here is the average Morrowind gameplay experience: https://youtube.com/watch?v=MkZ128eFT7U

+1 for Morrowind.

I would say Morrowind over Oblivion. Mainly because the towns are open to the player. I think this makes the most sense. But to each their own. Oblivion does have character physics...wink wink. So maybe thats a modders dream, I dunno.