Depends on your space, taste in games, and skill (and interest) in fixing them vs. playing them. If your interest is primarily in playing, and you like modern games, pick up 2 or 3 Stern pro models or WPC titles used (not the repros), don't spend money on toppers or other stupid, useless mods, and just play them. Then rotate them out for others once you're sick of any of them. If you lock in on one title and put a bunch of extra money in it, you'll tire of it (whatever game it is will get old).

If tinkering/fixing is half (or more) of the fun for you, pick up some older games (70's - early 80's).