what size plane and budget are you looking at? petro is generally more expensive overall. (yeah the fuel is cheaper, but the plane you put it on isn't, as well as the extra cost for the engine)

petro engines are somewhat easier to run, they generally don't need needle tweaking all the time, and assuming mag ignition, you don't need any extra batteries to start it. glow engines aren't much of a problem if you understand how to break it in and tune it correctly, they will run just as well as a petro. glow engines are FAR ahead of a gasoline engine as far as power/weight, at least until you get up into the really big ones.