I am quite happy with my classic systems. They run all the old software natively. If I wanted to run them emulated I'd just use UAE rather than AOS 4. I've got a Mac Mini running MOS, which is nice. I run AROS through VirtualBox, but in the end it's only the classic systems that feel Amiga to me.
I haven't used MOS so I wouldn't know. AROS on the other hand doesn't feal very Amiga to me at all. To me AOS 4 works just like AOS 3.9 but with lots of improvements and old software runs really fast now compared to my a4k with a CSPPC.
I feal that I'm sounding like some salesman which I'm not but I'd really like for those who's had a bad experience to give it another go. I DO think that AOS 4 should work just as well as AOS 3.9 with the hardware though but if some old hardware doesn't work it shouldn't be the end of the world, it might be impossible to write drivers because of lack of documentation.
Once again, I'm happy with my amigaone and aos 4, it didn't feel too bad going from aos 3.9 to 4.0 even though the first versions had lots of issues. Now it works pretty well though and feals just like my a4k did with PCI expansion, voodoo 4 graphicscard, fastata III and what not but better in every way. Sure SOME software doesn't work natively but you might be supriced by how much does and it's way faster too. It isn't like runing UAE AT ALL. You run old programs in MOS in the same way you do in AOS 4, there's no difference, With AROS there is.
If you're used to AOS and been using it up to 3.9 then 4.x feals like a natural step forward. At least it did to me...