Graphics Card .. Which Vendor Has Better Compatibilty?

Graphics Card .. Which Vendor Has Better Compatibilty?

I plan to switch from Windows to Ubuntu in the next few weeks.
I currently have a Radeon HD6970 in my system, that I'll be changing
during this process too (since it is loud and I can't make much use of it
under Ubuntu, considering that many of the more demanding games I play
aren't available anyways). Thus I'm looking for a card that is both
passively cooled (so it'll be silent) and that will play nicely with
Ubuntu.
It seems that currently the "fastest" passive/fanless Cards are the Nvidia
GeForce GT 640 and the AMD/ATI Radeon HD7750. Both have similar prices
(around €100).
Originally I was going to opt for the Nvidia one, considering how everyone
seems to claim that Nvidia has the better drivers, plus, with my
multi-monitor setup the driver in the live cd (12.04) for the HD6970 seems
to be crashing when I change the display setting (this is probably
fixable, but I haven't really had much reason to really look into it). But
then I read around here and on other pages that while Nvidia has the
better (as in better-performing; closed-source) drivers, AMD has better
(as in better compatibility; open-source) drivers that are updated/patched
more often.
So I'm not really sure which one to pick. While I don't really care about
the performance difference, I also can't really verify the better
compatibility of the AMD cards. I've always had AMD/ATI cards up to now,
and tried Ubuntu on/off a few times .. and the graphics cards have always
been a hairy detail (especially since I have a 2-monitor setup)
Any suggestions/ideas on which I should pick? Or is it even worth trying
both cards? Like I said, the deciding factor here is which one will cause
me less headaches. (Since performance-wise both cards are probably fine.)