The A4000 would be a better choice if your going to expand it. the A4000 has ZoroIII slots and are faster. The onboard IDE interface in the 4000 is also faster.
Just to add to what has already been posted,
What do you want out of the Amiga? are you just playing games if so the A1200 would do you just fine. The Cyberstorm for the A4000 is a supper eccelerator and with SCSI its even better these are pricy as they are tough to find where the Blizzerd for the 1200 is easeyer to find and thus costs less.
