IMO AROS isn't very usable as a standalone OS yet.
It depends on what you want to do, really. If you're fine with the software available for AROS, then you're ok I suppose. On the other hand, if you want to run original AmigaOS software or games, you'll need to obtain the ROMs (they're available legally thru for example
Amiga Forever) and use UAE.
(I'm sure someone will promptly point out the existing bounties for some projects that will supposedly remove the need for the KS ROM and allow transparent emulation. But until those bounties are completed this is the situation.)