Nitro is alot of fun, i can't speak on behalf of the Gas trucks, but from what i have seen they seem to be a bit more "tune and forget it" than nitro.
nitro does have a bit more of a learning curve than electric, but once you learn it, it is really easy. just expect to have to learn it, and the biggest thing, is if you have any questions or don't know, ASK, there are no dumb questions.
as long as you are using good fuel, and maintain them as necessary (i.e. gaskets being in good shape, fuel lines good shape, glow plug working properly, air filter cleaned) they should be very consistent for running. also make sure to watch some videos for tuning, JQ has a great tuning video, there is a good one from HPI for the savage (applies to all nitro still though), and a few others.
one of the biggest thing is while still keeping budget in mind, dont cheap out too much, engine quality severely affects ease of use and functionality.