It would be great to know the inner workings of these two companies. Both are privately held. Newmar recently transitioned control from the founder, Mahlon Miller, to the son, Matt. So far so good. Matt seems to be keeping up the quality.
Tiffin is led by it's founder Bob Tiffin and there are three boys behind him in position for leadership. Bob looks like he's in his 70's now and will probably not lead much longer. How do his boys feel about Bob's practices? Maybe they agree with their father and will continue those practices, but maybe not.
I'd love to have the inside read on the financial strength and internal workings of both companies but it's simply not a matter of public record. Try to choose wisely.