Depends what you want to do. If you specifically want games and demos, you may mean AGA ones. An A2000 has ECS so can run OCS-ECS games & demos but not AGA. If you want more productivity and expandability I'd say the A2000, though others will disagree. The A2000 has tons of Zorro II and ISA slots, but you will never be able to expand it to PPC or PCI. The A1200 you can add (theoretically) a PPC card and PCI slots, if you tower it. But to do this is a major, major expense and the results can be mixed and frustrating.
Personally, I'd go for the A2000. Expand it to a nice retro system.
