Yes there are two drivers, but hardly anyone uses radeonhd any more and the normal OSS "ati" driver works with *all* the ATI cards and with 3D acceleration on a recent kernel. (except the very recent R800 which is 2D only atm IIRC).
Also, fglrx isn't too bad any more, the only issue I'm having with it is slow unminimizing with compiz which means I have to run it with compositing disabled. And it's updated every month, I'd hardly call that "infrequent".
I have 2 nvidia laptops, 1 has frequent text corruption with Compiz, the other doesn't recognize the right screen resolution and so I have to supply a EDID file via xorg.conf; nvidia isn't perfect either.
FWIW - I have ATI in my desktop *because* they release documentation, I used to use Nvidia.