I did all star and high school my freshmen year, so I am very familiar with this topic.
I am a varsity cheerleader, and at the beginning of my sophomore year, I quit all stars to just stick with high school for various reasons, one being that my high school team goes to about ten competitions, and are actually quite good. We do level 4 and 5 stunts and pyramids, and we have level 4 and 5 tumbling. We also go to nationals, so I don't mind just doing high school.
We do though have 5 girls who do all star on my high school team, for 2 different programs. One of the girls on my team mom actually owns one of the all star programs, so she usually works it out so her and another one of my teammates don't have to miss much. On the other hand, sometimes all of the all star girls have to miss practice, which pretty much screws us for pyramids and stunts.
I think next year our coach will make the girls choose, which I don't find to bad, because 3 of those 5 girls love high school cheer.