From my experience Matrox were always excellent at their TV out properties.. (such as the G400's which can be picked up for next to nothing.) but their 3D performance isn't that great.. (2D was amazingly fast for their time though, still keeping up with modern cards now!)
Next along I would say ATi.. they would be top here, but if you're after something cheap, Matrox's can be bought for cheaper now, if you're after excellent 3D performance too, then definitely an ATi card. As I was saying, next ATi cards but not the top cards for some reason, My Built By ATi 8500 (Retail) card had excellent TV-Out (for a PC's TV out..
) even on my high quality 10 meter S-Video cable, but my latest card the Hercules 9800 Pro is slightly blurry compared to the 8500 on the 10 metre cable. Put it on a 1 to 3 meter cable (which is more the reccomended length for S-Video) and the picture is as clear as the 8500.
Next down I'd say the NVidia's.. they've just always never had that great of a TV-Out imlementation in my opinion. That's the main reason I got the 8500 back when they first came out, as I knew I'd be playing lots of DivX / XVid bits from my PC.
As others have mentioned, quality will never be really, really clear on a TV, but you can still have a pretty good picture (I have a Flat 32" Widescreen TV I use my PC on.)
S-Video is definitely clearer than Composite (as all of the picture signal isn't combined into one lead then separated again at the TV's end.)
And NTSC (US) picture quality is pretty poor on all TV Out cards I've ever seen, PAL is much clearer and has much nicer colours. PAL is also higher resolution.
The one nice thing about NTSC is that it's 60Hz instead of PAL's normal 50Hz, but most modern TV's support PAL 60 (PAL at 60Hz), but I have never found a way of forcing the Radeons to 60Hz on PAL yet. I was thinking of trying RefreshForce or something similar like that.
Hope that lot helps out anyway