I'm not sure there's always one single correct answer here, but I would take the Prevost over the Thor in this particular case. Five years hence the Thor will be worth maybe $50k or so, and the Prevost will not have depreciated much if any more. The general comfort and overall quality would be better, too.
On the other side of the coin, any repairs (particularly chassis repairs) to the more expensive unit would likely be somewhat more costly, and one might well expect some minor and perhaps not so minor age related bits to wear out and need repair or replacement. There are tradeoffs to every decision.
If you're new to RVing in general, I would suggest looking for a comparatively inexpensive used motorhome to begin with and have the expectation that you will sell it after a year or two and get something more like what you really want. It's often quite difficult to figure out what things are important to you and what features you care about without having spent some time using and living in an RV. At the very least, consider renting one for a week or two before jumping in the deep end. If you find you don't particularly care for RVing, and some (strange) people don't, it may save you a good bit of money.