That is a tough question, because you must take into account things like opening theory, defensive techniques and theories of the time etc. But if you mean somehow getting these players together when they were at the top of their strengths, I would have to go with Fischer. No other player before or since has ever demolished a string of World Championship Candidate's 6-0 or won their country's championship with a score of 11-0 like he did. Kasparov may be able to beat Fischer today, but to beat the Bobby of 25-30 years ago, I really don't believe there is anyone that could beat him.

No, you don't need to learn every possible opening variation there is. I would suggest taking an honest look at your type of style, then picking no more than three openings at a time to become completely knowledgable about. Do the same for the white side and the black side. Experimentation and "training" games with a computer will give you an excellent feel for positions arising out of your choice of opening, and this gives an excellent foundation for a future chessplayer to build on. One thing though: the BIGGEST difference between very very good players and average players is their knowledge of the ENDGAME. Learn your endings and you will be surprised how much you improve.

We were discussing the position below from Steinitz-von-Bardeleben 1895. What was mentioned was that 16....Kf7 was stronger than the move played in the game (16....c6). Black may have been dissuaded from making this move because of the following exchange sacrifice: 17. Qxe7+ Qxe7 18. Rxe7_ Kxe7 19. Rxc7+ and then White picks up an additional pawn. Whether Steinitz had a stronger response than this, we will never know, however this line we know is safe for black, as he has 19....Kd6, 20. Rxb7 Rhc8! leaving white to defend the mate threat in which case Black gets in 21...Rc7 and Black is in an excellent position, with his centralised king and weak white d-pawn.