Corsair CS750M or RM750

I am doing a RMA on my TX750, which is having the twitching fan buzzing noise that seems to be a standard problem. Since the TX is no longer made Corsair is sending a CS750M but I could have them send a RM750 if I want after I questioned what is really the replacement for the TX series. However, I can't seem to find any good breakdown of any quality differences between the Corsair CS750M and RM750. I understand the RM750 is fully modular compared to the semi with the CSM. From what I can tell the RM is a minor step up from the CSM. Given the choice what should I go with.

Corsair CS750M or RM750