drivers - 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.)

This is a really diverse topic, but I would go with the AMD card, because I had a better experience with AMD graphics cards when setting up multi-monitor setups using Ubuntu. But this can probably be different for you.

What's really good about AMD is the open source driver as you noted. The Linux kernel 3.11 features a new version of the AMD open source driver, which makes it really usable. I have it running for a week now and all my problems with linux graphics have disappeared. Unfortunately the 3.11 kernel is only available in Ubuntu 13.10 which is currently only available as a daily. In my experience it is really stable, but if you want to stay with the stable release, you probably have to wait until October to get the new open source driver. Before the new version I would strongly recommend the closed source driver.