Two entirely different things. Not even comparable, IMO - outside of the "Amiga-like" experience they share.
I've never had luck with AROS. Never, ever. I have no old machines, only modern, bleeding edge technology ones and have never had a stable AROS experience with them. Last time I installed AROS it thrashed a hard disk so badly I couldn't even fix it with Spinrite.

Those that do/can run AROS enjoy it, though.
AmigaOS requires specific hardware (A1, SAM boards, X1000, or PPC powered legacy machines) that is far more costly than what AROS requires, though. I have a SAM 440ep and the machine is damned near bulletproof and is a lot of fun to use.