I'm really fond of EM multiplayers, particularly 2-players. They are the most social of all pinball machines because each player only gets to play one ball while the other watches... and it's usually a short wait! Quite unlike the poor chap waiting for his turn on LOTR!
We already have a good thread on Pinside about the "Best EM Multiplayers". BUT - which ones hold up fairly well by themselves, and which ones desperately need a second player?
Of the ones I've played (or own), I recall these are pretty much as fun to play in solo mode as with others:
Out Of Sight/Far Out
....but these weren't so hot playing alone. Multiplayer or bust!
Nags (edit: oops! not a multiplayer!)
Solids N' Stripes
Snow Derby/Snow Queen
Any others come to mind? I suspect some of the multiplayer ratings on IPDB/Pinside are probably too low because they were only rated in solo-mode.