I only need a small car loan of 5-6K. Should I get a car loan through a credit union or a bank?

Credit unions usually will give you a better interest rate, that is pretty much the only difference.

I only need a small car loan of 5-6K. Should I get a car loan through a credit union or a bank?

credit unions will usually give you the best rate

I only need a small car loan of 5-6K. Should I get a car loan through a credit union or a bank?

I agree, credit unions are generally more competitive with their auto loan programs. I'm not sure where you live but the one I used for my car loan was Pacific Service Credit Union in San Francisco.

I only need a small car loan of 5-6K. Should I get a car loan through a credit union or a bank?

I suggest you to buy a 3K car instead.