Unless you're a professional welding inspector and cut the frames open and put them under an electron microscope, you're not in a position to evaluate the welds. I know this because I once said some years ago to one of my welders "nice welds" and he said "How do you know?". Thankfully, I wasn't stupid enough to reply "Because they look pretty!"
From a practical perspective, honestly, (I'm assuming you own a shop or something - can't think of any other reason why you'd want three Somas) what you're really interested in is "Which is more sellable", right? Whoever it is that makes Somas from where I'm sitting would only make the switch if a) There was some supply or price or manufacturability issues or b) The use of Prestige would carry more credibility/saleablity in the eyes of the consumer.
However, I'm guessing that telling a customer "Well, it was cheaper and easier to weld than 631, and everyone seems to think it's retro cool, so what the heck" probably won't work.
