I'd recommend getting an unlocked 1520 if you decide to get the 1520, so that you get many many more updates then the carriers will push. A friend of mine has a 1320, so I've gotten to compare the two directly (myself having a 1520.3) and while the 1320 is a gorgeous device, I'd still say go the extra mile and get the 1520, the 1520 still has an amazing battery, and man that camera is phenominal! I got my 1520.3 for around $400 new, I don't know if your looking for a contract pricing though, but if you can shell out the money to buy it outright, Id definately say look for a 1520 online, if not, the 1320 is still a great device that would perform similarly to the 920, though, I feel it would be a bit more like a sidegrade then an upgrade performance wise.
If you have any specific questions, feel free to ask!
Edit: I'm also gonna go ahead and add that the 1520 is the absolute BEST lumia made, not going by opinions, its the only high end lumia that has everything with no compromises, the only agueably better windows phone is the htc one for windows, but in my opinion, that slightly upgraded chipset isnt worth what you lose