Fave: Without doubt, the CD32. Small, perfectly formed and most fun to use Amiga I ever owned.
A close second would be my Franken1200, which gave me many, many years of service through numerous upgrades and hacks.
Least: A500, because no desk I could get a hold of that fitted in the front room was able to provide adequate space for the thing. That and the fact that floppies wore out, usually on the last disk on a long game that you were but moments away from completing.