In the long term, AROS is the most feasible. OS4.x is based on hardware that does not have a future roadmap. MorphOS is based on old Mac hardware which is limited in quantity. AROS is based on hardware that is plentiful and has ongoing development. I've tried the latest versions of both ICAROS Desktop and Broadway and they have really come quite a way from their beginnings. They are becoming more stable with each release. And the support for hardware is great. I have ICAROS 1.2.6 on a Dell OptiPlex GX280 with 3.2 GHz HT CPU, 2 GB RAM, 80 GB HD and an NVidia GS8400 512 MB PCI-e video card. The built-in AC97 audio works. Even the DVD drive is recognized. I got a cheap 3COM NIC for networking. I run it on a 20" WS LCD screen in 1680x1050 resolution.
On the software side, OWB works pretty well, but could be a bit faster. MPlayer is nice. I would like to see a decent office package. Right now, i just go into Janus-UAE, where I installed my old productivity software to do office stuff. There is actually quite a lot of software for AROS now. Hopefully, printing support will come soon.
And the other cool thing which I don't see on others, is pull-down screens just like the classic Amigas. Pretty cool, and actually quite useful.