hmmm...you've picked some pretty good ones there, Panchito! personally, i like WL best out of all of them. Poly is ok, but to me the original resorts are classics...but because they're a lot older, they kinda have a funny smell. i like the newer resorts much much better. but Poly definately has the more relaxed/private/romantic flair to it, over WL. and trust me, i've been on WL's beach at night...it seems like there should be a sign just before you get to the beach that should say something like 'Caution: Kids Run Amuck'...especially when the ancient water parade is about to start. and WL's beach isnt' that big to begin with, not to mention having all those kids run around. not exactly my idea of a romantic evening.
now, i don't really know about Poly's beach. i imagine with them having a tropical theme that their beach would be much larger and spacious...but i've never been out on their beach, so i wouldn't know about it.
ummmm, lemme see....oh yes. my take on Yacht/Beach. well, for me, it's a nice place to visit, but i'm not sure i'd want to stay there. for some reason the place seems like a hotel the Howell's off of Gilligan's Island would stay at. hence, it's a little too ritsy (sp?) for my country bumpkin self.
lol
so basically all this amounts to is that it's all up to your personal preference. WL has a great relaxed atmosphere...Poly has that classic tropical romantic feel...and well, the Yacht/Beach has a, um, 'rich people' feel (i don't know any other way to put it) but as it sounded from your first post, you've already seen these resorts...am i correct in assuming that?
oh, and if you haven't thought about Animal Kingdom Lodge, you might want to check that out via internet and take that one into consideration as well. i'd imagine standing out on your balcony, watching all the animals would be kinda romantic as well.
btw, just out of curiosity, has your fiancee ever been to WDW?