Here is a chart showing the difference floating around the net
I found out about this for the first time when Watchmen came out at the AMC Burbank 16, my friend asked if it was the same and they said only in quality not in size. They're wrong. There are 3 different AMC'S in Burbank so it can get confusing. The best is still the Bubank 16. Aziz Ansari of Human Giant and that new stupid show he's on fame found this out when he went to see star trek there. He was pissed and wrote it in his blog and thats why it recenlty became popular. Human Giant just used the 16 for their twiitter during a movie event. They saw Crank 2 which sucks so no harm done, plus they stayed in the back not to bother anyone.
Anyway back to the IMAX problem, don't go to any other of the IMAXes except the one in Citywalk and at the Bridge the rest are a waste of money. I would suggest going to either of the Arclights if you want a great theater. I'll have upcoming post of the best theaters in LA soon.