OK, so Screamin' Eagle at SFStL seems to be getting mucho thumbs up...
I'll add my vote to that one. It's the best big John Allen I've ridden. When you get to the far end turnaround, you just feel like you've travelled a long way from the station, plus it's a great setting.
As far a small John Allens go, I'm tempted to say Skyliner, but really it's all about the killer back seat first drop for me, there's not much else going on. So I'd have to say, of the ones I've done I'd go with Zingo. Good allrounder, couple of pops of floaty airtime and if I remember right, fun laterals in the final turnaround.