Trackballs are nice but they are very space consuming. What I highly suggest is to space the two players as far apart as possible but still close enough to see the screen clearly, because the best way to play fighting games, etc. is when both players have a comfortable amount of shoulder room and can still stare directly at the screen. Also if you are limited on space with your cp, you might consider swappable control panels, because my guess is you're going to be mostly playing one style or another in a sit down session aka: a friend comes over for fighting games, so you play with 2 joysticks, 6 buttons for that night. next day you want to enjoy some centipede and missile command, switch it to the other panel. So best way for you I'd think is one fighting game panel, and one trackball/spinner panel. And swappable controls is really easy, just search the forums or the tutorials on it and you can find out all the info you need.
-good luck