My first to EMs were Gottliebs, then I got a Chicago Coin which seemed a little intimidating. I think the documentation was more different / strange than the actual components or circuitry. In a perfect world (i.e. bigger basement) I'd have a few of each manufacturer. I love seeing how different manufacturers did things uniquely (or not).
I've been able to play Flip-Flop at a local club and it's a fun machine - I imagine the flip-flop mechanism are pretty interesting / novel.