Personally if I wanted an expanded Amiga the model I would choose depends on whether I had a need for 24bit graphics, 16bit sound, VLAB Y/C or VLAB PAR, GVP Impact Vision 24 etc etc or not.
Also the keyboard on the 500 600 and 1200 is quite bad....probably worse than the cheapest PC keyboards I've ever used in my life.
And towering an 1200 is a headache too.