RM-937 is for the European market and will not have the correct Class(es) of LTE in the Firmware for use on AT&T.
RM-938 is for the Latin American market and does have the correct Class(es) of LTE for AT&T. Additionally there is the extra 1700 MHz Band on the 3G/H+ radio that RM-937 lacks. By all accounts in the 1520 forum it does fine on AT&T. I know I have no issues with compatibility on T-MoUS and enjoy LTE daily with my 1520.3.
In all other respects the 2 variants are the same. Qi charging built in, 32GB internal storage on every unit, etc.
Why not visit the 1520 forum and read some accounts from users?