I about died playing the Ark multiball on Stern's IJ the first time I got it... I can only imagine someone dropping a loaf in their pants the first time they get 13-balls on A13 if they're not expecting it, lol. Hopefully I'll get that chance at some point..I've never played it, but it looks awesome.
I'll say that for the bang for the buck, multiball on Shuttle is way more fun than Pinbot's IMO...it's the 3 ball vs. 2 ball thing IMO. Keep in mind that my Shuttle has a worn playfield that affects ball travel, and neither machine is leveled correctly, lol. I dunno. I just find the shot more satisfying with the rolling jackpot value than Pinbot's lock/lock/lock/ramp/lock/ramp deal. I love Pinbot, but just based on multi alone? I'd pick Shuttle over it anyday.
*edit* I totally don't get the love for Firepower. I've played it on the PS3 a lot, and it just feels like it's an extremely basic and kind of slow-going pin to me....I've gotta track down a real one and give it an honest chance, but....meh. It will only be out of curiosity's sake to compare to the emulator version. I don't feel like it's something that will convert my opinion of it. =\