Glen Ellyn, IL
That's a tough one.
IM - short ball times. Can be great to keep if you have a bunch of games with long play times.
Tron - spectacular game. The sound and simple rule set keeps you coming back for more.
MET- awesome game play. Can't stand the music though.
TWD - great strategy game. Takes a while to grow on you. Read the rules though. Very deep.
For me it would be IM. You can always pick another one up cheap if you want another one. Or build an addition on to your house and add even more machines! 
