Basswood is neutral-sounding and works well with high-output pickups. Alder and poplar are a little brighter and will give a full, balanced tone similar to a Fender Strat. Maple is very bright and also very heavy in weight (unless it's soft maple).
Having said that, assuming your guitar's going to have a Floyd and a bolt-on neck, the body wood will have less influence on the tone than it would with a set-neck, fixed-bridge guitar.
What I mean is, don't feel you have to get a mahogany body - an RG-style guitar, even a mahogany one, is always going to sound very different from a Zakk Wylde Les Paul. Basswood's probably been the main wood used for RG guitars over the years, and they seem to work pretty well.