I've tried Federal 209A, Remington Kleenbore, 777 primers & the "Vari-flame" primer system that allows you to used small rifle primers in a 209 setup. After a lot of testing, in my rifle these are the most accurate in order:

1. 777 primers
2. Remington Kleenbore (usually pretty accurate, but seem to get flyers sometimes)
3. Federal 209A
4. Vari-Flame system

The Vari-Flame system might have the potential to be very accurate, but I had a lot of trouble with misfires and noticeable lag times between when the primer went off and the main charge went off. These issues caused me to flinch or move sometimes and threw off accuracy.

From reading posts on this site, it seems like every gun can prefer a different type of primer. You almost need to buy a couple different kinds and compare them side-by-side in your gun.