I like the 626 shape better personally... but shaping is personal preference. For what it's worth, I have a Roma (lucite) in the 315 KS shape (prince). I like modestly bent and I like apple-esque shapes the best.
I don't know that either of those shapes is iconic/quintessentially Savinelli shaping, so just pick whichever shape appeals more to you. I also agree that the 320 is probably their most quintessential shape, but I personally don't find bloated shapes like that appealing (the chonkiest I will go is like a Chacom 871).