You gotta consider defense and batting order dynamics as well. You prolly wouldn't fill you team up with nothing but slow, power hitters for example. You can also pick players to play different positions if you want, for example one could put a center fielder in left or a SS at 2B if you want.

1. Ty Cobb, LF (greatest hitter for average ever, good speed, stole a lot of bases, not a ton of power, good defense for LF)
2. Willie Mays, CF (good hitter, good power, good speed, good defense, good at it all)
3. Ted Williams, DH (Best hitter ever, slow, doesn't need to play the field at DH)
4. Hank Aaron, RF (Great hitting and great power, decent defense)
5. Lou Gehrig, 1B (Great hitting, great player and teammate)
6. Honus Wagner, 2B (Great hitting, good speed and Defense)
7. Mike Schmidt, 3B (Great defense, good Power, just ok average)
8. Ivan Rodriguez, C (great defense, pretty good hitter for catcher)
9. Ozzie Smith, SS (great Defense, good speed, back flips, not a great hitter)

SP Bob Gibson
CP Mariano Rivera