I'm one of the few that loves the look and the small size of the A600. It's perfect as a games machine. 99% of the classics aren't AGA anyway, and with a decent harddrive and accelerator, it's an excellent games machine if sexed up with WHDload.
EDIT: on the other hand, it looks like you're missing an AGA Amiga, so I'd go for either the A1200 or A4000 (which I really really want). I say the A1200 'cause it's so damned sexy.