A500 all the way for me, it's just a 'classic' case and you can spot it a mile off.
A1200/600's are nice cases but always felt flimsy in terms of quality compared to the 500.
1000 would be my second choice, very well built and well thought out with the keyboard garage/mouse & joy ports on the side and somewhere for your monitor to sit
3000 desktop would be third - probably the nicest looking of the desktops but lacking the 1000 originality so is 2nd...
2000/4000 are basic shapes and too IBM'ish in looks for me although it's whats on the inside that counts
CDTV/CD32 - CDTV would easily win due to a nicer quality finish, shame the cd32 never came in a nice chassis like the CDTV