I always like to snap roll at the top of a loop. From there i can either finish the loop or fall out into a spin. When done properly and cleanly, they are very impressive maneuvers. I have always wanted to do a loop with a snap 1/4 up, at the top, 3/4 and at the bottom. I imagine this would be a very hard maneuver to do, but i think it would look sweet.
If you are just learning how to do them, start at half throttle, and with lots of alt. worse case scenario, you over rotate and end up inverted and heading for terra firma. Once you get them down, try and do 3 or 4 in a row. Its very hard to do right, but it looks great. I just love stalled maneuvers.
when i try new things with a snap, i just use full elevator and full rudder. It slows it down alot and makes it easier to end the snap where you want. Most full scale planes dont use aileron to do this, except the edges and yaks, ect...
Snapping this way also makes you loose almost all of your "E" at one time, so you need quite a bit of power if done in a veritcal maneuver.