Is GMAC mortgage a good company to do business with?

I signed up for a home loan with them. I have read reviews of GMAC that make me question my decision. I realize that i should have discovered my concerns earlier. Does anyone else have a loan with them and has the experience been positive? Any suggestions on whether to prepay points or just keep the rate as is? Any ways to get a loan with less than 20% down and not pay P.M.I.? I heard either get a 80/20 loan or agree to pay a higher interest rate and get a larger loan which includes the P.M.I. costs. There has to be another way.