Once again, it depends on what you want it to do.
If classic gaming is important, UAE is probably the better choice. It tries to emulate all Amiga custom hardware. UAE (and Amiga XL) are hosted in another OS. Some ppl hate this.
If you cling to Amiga for other reasons (philosophical, elegant OS, love the productivity apps, etc), there is a lot to explore and appreciate in Amithlon. Like Aros, Amithlon "feels" like Amiga OS was ported to X86 architecture and is natively running, though, it runs in a small kernal.