I had this exact dilemma a few months ago. I sold the A2000 and kept the A3000.
As I see it, the only advantages the A2000 has are an internal 5.25" drive bay and better support for bridgeboards or RTCs.
The A2000 has lots more slots, but only 5 Zorro ones. One more than the A3000, but you've probably used the extra one for a SCSI card anyway!
With some jiggery-pokery, you can swap in an ECS Denise and 2MB ChipRAM on an A2000 and have full ECS support, but the A3000 comes with this as standard.
Just my 2ยข on the matter.