The 1000 is best by most meanings of the word "best."
Perhaps you meant to ask which Amiga is the most expandable?
*edit*
You also didn'tsay for what expansion. I saw a guy with a 2000 the other day with a 486 card, macintosh card, sound blaster, VGA card, NIC, Apple IIe card, RTG card, 060 card, and I think a toaster. He said he used it for retro game shows becuse it could test IBM, Amiga, older Mac, and Apple 2 disks using one box. I think the Amiga has a 300watt PSU and more ISA slots than the 3000 or 4000, (but maybe not the tower.) So for that purpose I'd say the 2000 may be the "best" machine.
