I've stayed at all 3 resorts and I think it comes down to your preference. If you're looking for a "Disney" experience I'd opt for either POFQ or POP. Royal Plaza is a fantastic hotel, and has quite possibly some of the most comfortable beds I've ever slept on, but the Disney magic just wasn't there. That was okay though for me at the time. I was 22 and it was a long weekend, girlfriend trip.
Out of POFQ and POP I'd go with POFQ any day of the week. I love it there. It's small and nicely themed, and allows guests to take advantage of all that POR has to offer. I've only stayed at a value once, that being POP, and while it was nice it was just too large, noisy and busy for me personally.