So, I have changed from an ATI X1600 Mobility to an Geforce 9600M GT...
VDPAU is nice, when it works.
I have suspend-resume issues I never had with the ATI.
Wine games do seem to work better.
It is 3 years newer, and only twice as fast
I also have issues where every second driver breaks my screen brightness controls.
I have played on a notebook with a 4650 Mobility, and yes, in windows it is over twice the speed. It also seems to use less power, and run cooler.
Personally, based on my experience, with the current FGLRX (Only real issue is 3D games in Wine are less compatible, and stay away from Xv) to the NVIDIA where the drivers bring down the system (and appear moody).
I can't recommend anything, but NVIDIA is not from heaven. And I am really starting to get pissed off at NVIDIA's "We can do no wrong" attitude. Surely my next system won't have NVIDIA in again, but that is more a political issue.
wine always runs slower with new dx9 games. i would guess only 50-60% of win speed. for demanding games with slower card it is usually too slow. ati would be faster in win and but fewer games run with wine.
Choose AMD/ATI. Opensource drivers work well, now beginning to support 3d acceleration beginning with mesa-7.6 kernel-2.6.32 radeonhd-1.3.0 .
If you prefer fglrx drivers, they work splendidly and have the once a month update just like the windows drivers ever since AMD bought ATI. I have owned nothing but ATI cards all my life beginning with rage3d, and havent' had as bad of issues as everyone makes it out to be. yes, there WAS crappy support, but no longer. That is all a thing of the past. AMD/ATI has better support than Nvidia now thanks to opensource driver funding and actual monthly updates.
Nvidia is fading, and isn't the shining star like back in the old days. AMD/ATI has always been pretty innovative and has had a lot of firsts in the industry. I own X200m, HD2600, HD3300, HD3650, HD3870 OC edition and have never had a problem. I remember x200m didn't work with Opensource drivers but there was fglrx until the opensource drivers worked, then the switch was simple. I'm soon to be the proud owner of the HD5870 series for my new OC phenom II 4.2ghz 955 BE 4GB 1600mhz DDR3 dragon platform box.