Gas is still the way to go for a trainer. You can get a bigger, better flying model for less than the equivalent electric.

Electric has come a long way in the last few years, and IMO is the future of R/C. The massive growth of suburbia will result in more pressure on R/C clubs to curtail noise and this will lead to faster development and acceptance of electrics.

Electric power is probably where digital photography was in the mid 90's--set to make rapid gains and eventually all but replace internal combustion engines as a power source. (Interestingly enough, almost the opposite has occurred in the R/C car arena. Electric power was king of the hill ten years ago, but now "nitro" cars are the big thing.)