Lots of MIDs go w/NFCU b/c there is a branch on the yard. However, I've heard parents and mids say great things about USAA as well in terms of banking.
My personal advice is that your mid should set up an NFCU account, even if it's not frequently used. It doesn't cost anything, NFCU tends to have branches at most USN/USMC facilities worldwide, and they do offer a lot of good stuff (loans, etc.) for down the road. You can have accounts at both NFCU and USAA altho one obviously must be your primary.