How do I choose who to get my mortgage through? Major banks or smaller mortgage companies?

hmmmmm questioned: I have an established relationship with Bank of America but there are several other smaller banks and lenders out there with better rates. What happens if you get a mortgage through a smaller bank or lender and they go bankrupt or get bought out by another company? Does it affect your mortgage rate? Is that the chance you take or is the rate locked in no matter what?