Bobby Fischer for sure.
the best chess player ever
I am going to go out on a limp and say Botwinick (please someone tell me if this is spelled correctly). No other player defeated so many different world champions. He is also the all-time most influential player founding the soviet chess school. But comparing players across history is not very meaningful do to different times they played in.

Must be Kasparov for two reasons.
He was dominating the chess world for almost 20 years (wich is long):
1. At the time when the level of play was highier than ever before.
2. At the time when the level of competition was highier than ever before.
At the present moment there are almost 1500 living Grandmasters! If you consider chess as the ability to make good moves, I'm pretty sure that most of these Grandmasters play the game better than some of the early World Champions. Present GM's can just make better moves! Because of the knowledge they have and because of more professinal preparation and more advanced training methods.
Now about competition. Even at Botvinnik's time how many GM's were there? Around 30 (I belive).
Being overwhelmigly best for a long period of time amongst hundreds of very very good players might look even more impressive than being the best amongst 30 very very good players.

hi, what do you think who is the best chess player ever

Borislav Ivanov has played some great games, pity he quit.
He did have a very distinctive style... :)

He used to announce things like "mate in 7" at the end of the game too. He was a class act all the way.... :)

Anatoly Karpov is by miles ahead of everybody else. Then comes the other Great Soviet Communist champion Kasparov. Right after them comes another Soviet Smyslov.
The 10 best players of all time are all Soviet Communist Champions:
1. Karpov
2. Kasparov
3. Smyslov
4. Botvinnik
5. Tal
6. Petrosian
7. Kramnik
8. Spassky
9. Alekhine
10. Bronstein
In terms of who makes it to the top then, that's not particuarly controversial, except perhaps Bornstein. Bronstein?! in the top ten players of all time? Hard to argue with the other nine, apart from perhaps the order you've put them in. Kasparov did do rather well against Karpov in matches you know.
hi, what do you think who is the best chess player ever