Tableaux. High school players (in general) shouldn't take on the Ibert unless they are prodigies or something. It's the most important piece in the saxophone repertoire, and you should be very well musically (not technically) developed before you try something like that. Playing it poorly or incorrectly can actually set you back as a player because it is a piece that you will have to know at some point, and you want to learn it correctly the first time.
Plus, it's MUCH more difficult than the Creston, and if that's the level that you're at, you'll probably be able to play the Tableaux well, and might only BARELY pull of the Ibert. The fifth movement of the Tableaux is difficult, but not as difficult as the first movement of the Ibert, and it definitely doesn't have ANYTHING as hard as the cadenza(s) in the second movement.
As a compromise, you might try the Glazunov. I played that in high school, and it's usually the first concerto that most people play...