from what I can tell:
Balltops are good for twitchy type action (because of how one holds the ball on top, with their fingers wrapped around and the palm above). This is good for early arcade games, such as pacman etc et al...
Battops are good for games made in the 90's (fighters come to mind) as they are more ergonomical and a little easier to use in some respects.
I play mostly 89 - present arcade games, so am going with bat tops.. They just seem to make more sense with the game selection I intend on. Plus, the balltops almost look like you could snap them in half way too easily (I know this isnt the case, but psycologically it has an effect)
maybe we could make an index based on how hard a game is and attach a "balltop" or "battop" label to the game. This may not seem to be a good measure, but we all know that the earlier arcade games were much more difficult than the later batches. (Admit it!)