Megan pretty much summed it up, if your just in it for the experience I'd recomend the fernie comp, its real mellow(attitude and terrain wise) until the finals, the lizard head wall is pretty intence.
Also - I'm pretty confident that none of the comps have a junior division. You'd have to lie about your age if you're under 18 if you expect to compete. The only event that I can think of that has a junior division would be the US Extremes in Crested Butte, CO