Favorite Amiga: A500 because that's the first one I owned and did the most programming, gaming, music, drawing and everything else on in those days. A1000 would be a close second just because it's the original one I saw in 1985 in a computer store. I still have it.
Least Favorite Amiga: I don't have experience with every amiga model so I couldn't tell you. They all seem to have their purpose. Maybe the A500+ because it broke compatibility with the 500, right? Life was easy in the early days when there were just the 1000, 500 and 2000.