"Best" is a very subjective term.
To purists, the Amiga 1000 is the best, since it is the original Amiga.
The Amiga 1200/4000 appeals to those looking for the most technically advanced Amiga. These two come close to matching modern PC's for capabilities.
My personal "Best" is the A500/A2000 duo. This pair represents the high point in the Amiga's history. Amiga was still ahead of the game for price and performance, and Commodore was at the top of its game. I like the A500 for its profile, and the A2000 for its tinkering factor.
It's all subjective, and it's all personal.