When we had our 2003 Suncruiser 33V we determined that what we really wanted was a diesel pusher. Our local Itasca dealer was also a Newmar dealer and looking at Newmar told us that it was a higher quality RV. We had a good relationship with that dealer and he was only 5 minutes away so it was kind of a no-brainer.
In our process we had narrowed it down to being a 40' Dutch Star. We drove them, spec'd them until we were blue in the face, and researched everything to the point where we knew more about them than the salesman.
However, getting the perfect coach together never quite happened. There was always something out of place. Some options weren't available and some things came on them that we didn't like. We wound up paring down out exterior color and interior decor to the on we could best live with rather than one that really looked good to us. We actually started looking at a Mountain Aire to rectify some of this but the MADP was out of our price range and even the Dutch Star loaded with all the options was getting a bit high for us.
In the process we looked at a MADP at another dealership when travelling through Kentucky who also happened to have Tiffins. There we saw a 2004 Allegro Bus and really fell in love with it. All of the things that were missing in the Dutch Star just fell into place with the Allegro Bus. Furthermore we found that the Tiffins were a better value than the Newmars. You got more bang for the buck with Tiffin and even the dealer offered that advice to us.
Long story short - we bought a 2004 Allegro Bus from a dealer who was 2-1/2 hours away. It was a tough decision because we were walking away from a dealer who was 5 minutes way that treated us well. But, we were buying a coach, not a dealer, and the Dutch Star just never fell into place for us. We actually got a coach more in line with the Mountain Aire for less than the Dutch Star in price.
Again, these were personal choices. Other than the fact that you get more coach for the money from Tiffin, and the details better fit our desires, I don't feel that the Newmar was of lesser quality. Then again, I haven't owned a Newmar so I can't offer that from personal experience where others can. From what I could see they were both well built coaches from decent companies. That was in 2004-2005 though so if things have changes I can't comment on that.
If you are particularly fond of a certain model coach made by either of these manufacturers I'd say buy it because you won't go wrong.