the mk2 16-35 is supossed to be a significant improvement over the mk 1, I've only used the mk 2 so cant confirmI feel like anything past 24mm will be too long on a cropped sensor. The 24mm 1.4 would be fairly wide and be great for low light conditions with no flash.
However, with quinceaneras, I would imagine you are doing lots of large group shots with a flash. In that case, I would stick with the 18-135 or look at the 10-22 (If you are commited to using EF-S).
i was hoping to get an ef L lens but ef-s lens is not going to kill me. i was looking at the 16-35L II nice fast lens but little pricy is the mack 1 still available?