Before I begin, I've been a NFCU member for about 2.5 years. I was able to join through the Navy League, a method no longer used by Navy Federal. I orginally joined for the credit card, which I use still use regularly. I mainly bank at the CU for the great CD rates. Their customer service is excellent. I have never ever had an issue with a branch, associate, or the credit union in general. I have adjusted my banking to keeping a third of my money in NFCU, another CU, and another bank. I like having multiple banking options so I can max out on rates. Any reason is if the CU's debit or credit card system is down, I have another option.
The only issue I have is an extremely minor one is the fact that NFCU does not have an ACH method on the website to transfer money into your checking or saving account. It's not a big deal becuase my other CU does have unlimited ACH.
I personally Navy Federal is one of the best credit unions out there, with their great mix of branches, online banking services, and a great mix of financial products, next to no fees.