A credit union CAN be a great resource, and they can be tough competition to me, a broker.
However, each credit union is different and they oftentimes only do equity lines/second mortgages, it really depends who it is. Some do traditional mortgages as well. If you have access to one, definitely ask them.
A good broker or bank/credit union loan officer will listen to what you want but will also give his/her educated opinion on what you say you want, show you why something may or may not be better, and give you a couple options (30y, 15y, ARM, whatever) based on what you say your goals are. The key, though, is the loan officer will educate you to allow you to make your own decision.
Rates are important, as are fees and closing costs, but you have to consider both the short-term and long term of the loan - if you don’t think you’ll refinance again for a while, you’re better off to pay more points and take a lower interest rate in the long-term...if you are more likely to sell/refi/whatever in under 3-5 years (depending on your own situation, a good loan officer helps you figure this out) then go with a lower closing costs option with a slightly higher interest rate.