Most of my MP's are also MISB. I look for symmetry when displaying them but even for people like me that collect only from MP-10 onwards (ie when the scale changed) there is a lot of different box sizes. In fact I count 6 different sizes from MP-10.
In order of size:
Optimus Prime (MP-10)
Ultra Magnus (MP-22), seekers etc
Shockwave (MP-29), Black Optimus Prime
Ironhide (MP-27) and Ratchet
Prowl (MP-17) and other Autobot cars
Cassettes