First off - if you are competing - read your class description and you may get your answer there. Generally speaking a rest - especially a flipper and plunger - is WAY more forgiving. They are also very fine tunable. I know I pick up 10 points or so on an NFAA indoor target with one. Though in many cases competitive venues that allow elevated rests allow modern riser/limbs (carbon, foam, aluminum, etc) so you aren't going to be competitive anyway. Though some traditional shoots will allow an elevated rest.
When I'm hunting or shooting for fun I shoot off the shelf. I like the simplicity of it - nothing to worry about coming out of adjustment, get hung on vines, or need a tool to handle those situations. Off the shelf also tends to be easier to shoot in all sorts of contorted positions (when we play "follow the leader" once the shelf shooters get to choose it's easy to make it rough on the guys with rests). For me I like shooting from odd positions when shooting 3-D and the local traditional shoots do too.
So in short, for competition shoot the most forgiving and consistent thing you are allowed. For fun (be it at a tournament or on your own) - well none of us can answer that for you.