I don't think you can go wrong with either one. There were only two coaches we looked at when we went DP shopping. We wanted a true 40' with a tag, which eliminated the Tiffin. Now that we own the Newmar with Comfort Drive, I wouldn't buy a coach without it.
I do think that Tiffin does a better job on their paint, more coats of clear and heavier built bay doors. I know everyone says that Tiffin has a great warranty, but from years of reading the forums, it seems like many have had great warranty service, just a lot of it. Often requiring a trip to Red Bay.