Avoid Wells Fargo if you can. We went through them in Ames and it was a horrible experience. In most cases you aren't going to see a huge difference in rates, but the difference lies in how well they handle the process. In my experience, credit unions will generally go out of their way to help make things easy for you and explain the process. When we went through WF, they just told us to sign and initial without really going through the paperwork. We were constantly having to call and make sure things happened like the appraisal (which in the end didn't by the closing date).
While this may be just one bad agent, we were so turned off with them that we just didn't want to deal with them again
Once the loan is setup, I've never understood why it matters if they end up selling it. Just setup an automatic payment and you really don't have to deal with them again for 15-30 years.