Well, I've just gone through all of this myself recently when I got a 9600xt with VIVO. After a lot of trying everything I found that:
If you're using normal composite (yellow, red, white) cables then run your games in NTSC mode. Use Dscaler with 720x480, sharpness and gamma filters on, use tomsmocomp for deinterlacing. I found this to give better picture over PAL when using composite.
But then I got an Svideo cable and WOW! It makes a huge difference - if you have one, then run your games in PAL mode and use Dscaler with 720x576, and other settings as above. I found I had to increase the gamma a bit when running in PAL also.
Hope that helps.