Could someone give some info on these cards in Linux?

I hope to upgrade sometime and I think it's between these series of cards:

Nvidia 260 GTX and the ATI Radeon HD 48xx series, 4870? Whatever is available at the time I'm ready to buy that is under $200.

I want to support ATI so I'd like to choose it but I get the impression there are so many restrictions or limitations currently (still? :-( ).

You need to use open source drivers for 3D or gaming? Whereas, 2D is fine with the proprietary fgrlx drivers? As long as the Catalyst utility/drivers are updated or something?

Maybe game in Windows on Windows partition and then it doesn't matter which you go with either AMD or Nvidia? I watch movies or video a lot with my computer (Online videos, movies both DVD and .avi or mpeg/mpeg4 etc. etc.) so I was wondering how either ATI or Nvidia cards plus the respective drivers effect this. I know the older Nvidia cards are fine and probably newer Nvida cards are supported via proprietary/binary drivers. There's a limitation there but at least there is not as many video issues? Or is there some tearing in certain cases? Or does that apply to ATI (only?)?

Could someone comment, explain and compare (perhaps?)?

Also, if ATI's drivers have both pros and cons depending whether you're using the open source or proprietary and what you're using them for, 2D or 3D, can you switch back and forth easily or does it involve installing and uninstalling? If so, how complicated is that process?

I've only dealt with Nvidia so far.

Thanks in advance for any replies. Sorry, if this post became rather lengthy and if I could have summarized it with less wordiness, I did try to address all the various comparisons and topics as briefly as I could. ;-)