UAE (or WinUAE, to be precise) and a fast Windows PC.
AmigaForever is a commercial distribution of WinUAE, with lots of cool stuff added - most importantly, it includes legal versions of the Kickstart ROMs (these are required by every emulator) and AmigaOS 3.9.
AROS is not an emulator, it's a seperate, amiga-like OS for your computer. It's not able to run existing Amiga applications (yet), these have to be recompiled for AROS. In its current form, AROS is not really useful for desktop users, it's a nice (and free) gimmick though. give it a try.
