I'll put in a good word for the 3000. While it doesn't have the AGA chipset, it's a nice machine otherwise: compact but durable, easily exandable (with the faster Z3 bus,) and not nearly as sought-after as the 4000 (which means you can get it cheaper.) I got mine a couple months ago, and I'm already loving it.
1200's probably the nicest games machine, but the downside is that, like the other keyboard Amigas, it's a lot more of a pain to expand.