What kind of RG is it? If it's a 550 with a pickguard, I would mount them in the pickguard. Asthetically, I don't like pickup rings on superstrats so, if it was a 570 I would direct mount them, unless it already has rings, then it's got the holes anyway.
Sonically, it doesn't make a ton of difference (IMO, I know there will be disagreement). One of the arguments I hear for direct mounting is that it give better bass response, but in an old article with Steve, he said they decided to mount JEMs pickups to a pickguard because after trying multiple ways of mounting, he thought he got more bass when they were pickguard mounted.
yeah. 1570s are direct mounted. 570s have pickup rings.
one difference i've noticed is the amount of noise transferred through the body if the pickups are direct mounted. if you bump the guitar or move it and the cable rubs against it, it seems to pick up that noise more.
I've tried rings, pickgaurd and direct mounting and found almost no difference. Not enought to choose one over the other. Persoanlly I like ring mounted pckups better because they are so easy to install.