what's the difference between a C= A1200 upgraded with 3.1 roms and and an Amiga Technologies A1200?
Besides 3.1 ROM's and a PC floppy drive adapted for the Amiga, I believe that the AT A1200's motherboard is a later revision and fixes a few problems that Commodore never had chance to do.
Which one should you sell? IMHO, you should sell the Commodore A1200, simply because its an older motherboard revision. The floppy drive problem of the AT A1200 won't affect you unless you have lots of old games on non-DOS floppies which use strange methods of copy protection.
Steve.