They are basically the same device internally. Difference is in the screen (AMOLED vs LED), camera, flash, body design and internal memory (if you don't have 32GB option).
I also think that the 920 is overall the best value (mainly because of extra 16GB) because is much cheaper than the 925 and it is not much of an update. get the 925 ONLY if you really dig the slick industrial desing (altough there is nothing worng with the 920's design for that matter!).
While the L925 maybe is the better looking, i just love the weight of my L920. You just have the feeling every time you use it that its premium ( but thats me ).
925 is too pricey and it is not an upgrade from 920. Just add a couple of dollars and just get 1020. A good upgrade from 920 but If I were you, I would wait for the beast 929.