I would have to say:
A4000 for compatibility - it can run most older games through WHDLoad, pre-AGA machines can't compete because they can't run AGA software (obviously!) A1200 is a close second, but lacks the neatness of keeping most expansions inside the case without investing in a tower.
A1000 or A3000 for appearance.
A600 for neatness.
CDTV because it looks good in black, and because it was ahead of its time (I can imagine Commodore having released a DVD-based version had they survived!)
