Whats the difference in Majestic Class C's?

"Majestic" is what Cruise America brands whatever units they have contracted to be built. At different times they've contracted with different companies, presumably with similar sorts of specifications (these are not standard, off-the-shelf products that the companies otherwise produce). The difference between the Thor, etc. ones is just who built them.

In general, I would not expect vast differences in build quality between the Thor and Four Winds variants. I could well be wrong; I haven't studied the matter in detail at all.