I'm pretty happy with most of the newer USB audio interfaces, as they happen to be more and more class compliant, so you don't need a seperate driver for it. I'm using the Presonus AudioBox 1818. It works fine with Linux, but I can't use the internal mixing engine. Would be fine if that worked, but is not that important for me.
What I really like about Linux drivers is that if they work, they won't get obsolete so quickly. I've had more luck with old supported hardware on Linux than on newer Windows versions. I also don't miss all the crapware that comes with some Windows drivers. I am looking at you Nvidia - I just want my monitor to work, I don't need 10 tools for my third monitor.