Hi. I think I need to work on my positional chess aspect of the game and so I heard analyzing grandmaster games is a pretty effective tool. I want to pick a world champion or someone that's really good who's also very very positional. Who would you recommend? Thanks.

P.S. Do you know what playing style Fischer is?

P.S.S. What positional chess books would you recommend? I've read My system and Simple Chess

Tigran Petrosian and Karpov comes to mind, but let's not forget an oldie (but goldie) like Steinitz aswell.

Look into both Aagaard's and Silman's books.

Smyslov, Petrosian, Botvinnik.
Fischer and Spassky are regarded Classical players.
Probably Rubenstein especially in two famous games one against Lasker, the other Capablanca were positional games. Note that Soviet players studied Rubenstein games.
Chess at the Grandmaster level, the good Grandmaster level is about style.
Keres and Reshevsky played positional chess.
In the former Soviet Union, Boleslavsky, Bronstein, Taimonov, and probably Geller were positional players.
Kotov in the Soviet School of Chess, (a propaganda book) indicated the styles.

Oh, how could I forget one of my favorites, Botvinnik, his games are beautifull, I recommend them whole heartedly.

Yea Botvinnik came to mind first for me haha - very positionally strong player.

say, how do you know first whether a player is a positional player? Karpov is a positional player, i believe, but he also attacks and sacrifices when the position calls for it...

He attacks and sacrifices because he's a very strong GM. When the position calls for it any GM will produce attacking flurries.. How they usually go about winning chessgames determines their playing style, but it's never one-dimensional positional or tactical.

The tactical player wins or loses faster than the positional player!

I don't know if loosing as quickly as possible is necessarily a good thing.