1200s are vastly cheaper than the 4000s nowadays, they are very expandable, and the PCMCIA slot comes in very handy these days.
The 2000 can be upgraded quite significantly too, of course, and you already got the beast.
1200 advantages: AGA. PCMCIA. IDE.
2000 advantages: Zorro slots (but 16 bit), far easier to add RTG
this is not true,its a common misconception. by the time u buy a 1200 and add a accelerator,get a decent power supply because the stock one is crap,your usually around $300-400+ and you still have no good expansion bus,which is what alot of used stock A4000/040's run(if not slightly more) .grab a zorro3 machine with buster 9 or 11 chip and you are further ahead.
A2000 zorro2 is dirt slow.i love the 2000 but why bother with zorro2,it cripples the gfx cards.