We financed our latest vehicle purchase through Denton Area Teachers Credit Union and have not had any major problems with them. They were able to offer us an APR we simply could not turn down.
The only criticisms I have against them are:
1. They don't have a convienent branch location for us to business with them face to face.
2. You can't bank with them through a Credit Union Service Center.
This doesn't pose a problem now as we only have an auto loan through them. But it could if we were to open a checking account.