Yeah, I asked the same question several years ago, found me a sweet MVS-4 (ver. 2) and loaded up on carts!
... but, eventually, I couldn't handle an addiction to MVS and pinball so I sold a whack of carts, bought the 161-in-1 and saving 6 games NOT on the multi:
Baseball Stars Professional, League Bowling, Nam-1975, Ninja Combat, Shock Troopers, and Windjammers.
Btw, if you need new light panels, get them from Glow Hut: http://glowhut.com/a6-electro-luminescent-panel-with-leads-and-connector/. They're great.
Neo Geo, Neo Geo ... 4 bright buttons and two joysticks!
Quoted from benheck:Let's discuss ideal four slot loadouts!
My picks:
Neo Turf Masters (poops all over Golden tee)
Metal Slug
Puzzle Bobble (huge hit with the GF's at parties)
Then maybe a fighting game?