We recently did the Newmar/Tiffin comparison but we were deciding between an Ventana LE & Allegro RED. Both were very nice but there were some differences. We didn't get either one of those though. After a LOT of research and deciding what we wanted, we settled on a 2011 Newmar Ventana.
Side by side, it seems the Newmars are a bit heavier and can carry a larger cargo. Tiffins seem to have more cabinet space but are a bit lighter and the cargo capacity isn't as large.
In my research, I found that there were a few years that had some issues for Tiffin. You may want to research the "Big Three" which are problems with the roof, slide floors and the wet bay. I *think* the years was around the 2010-2012 models but I won't swear to it. The interior workmanship seems to be of equal quality.
We liked the floor plan of the Newmar 3433 and since we were concerned about the FWS in other models, the 4 slides of this coach really appealed to us.
Flip a coin!