Favourite has to be the A2000 due to the fact that it is built like a brike-poo house and has so much space inside that you'd never need to put that mobo into a tower case.
Least favourite Amiga that I've owned has to be the A3000. It has the potential to be so good, but that crappy case design was just too small. Designed by an artist rather than an engineer.
Then there's the A600 which is the one Amiga I've never been tempted to own because of the missing keypad. Launched just before the A1200, I know several people who dumped Commodore after buying one because they felt ripped off by the quick arrival of the superior A1200 and were not prepared to hanf over more cash to buy the machine they should have had to start with.