I can't help with the B Resort, as I haven't stayed there. I do have a reservation for New Year's, though. I'm pretty picky about my hotels. I've done research and walked through the place when I've stayed nearby. I'm confident it'll be a nice place to stay.
I've spent 50+ nights at the DoubleTree Suites over the past several years. I've never had a bad stay. Any minor issues (bad TV remote, in-room safe malfunction) where easily fixed with one phone call. It's a solid hotel with an above-average staff.
You may already know, but these two hotels are adjacent. So, there's really no difference in location. I think the DoubleTree Suites will win a battle of room size. All the rooms are 540 square foot suites. (For comparison, that's roughly the size of two Disney Value Resort rooms.) Virtually all the suites are "wide" instead of "narrow". By that, I mean both the living room and bedroom have windows. I find that configuration preferable to narrow rooms where only the bedroom has windows and the living room is dark.
For a shorter stay like you have, the extra space of a two-room suite might not be worth the extra $100. If I were in your shoes, I'd almost certainly switch to the B Resort. Other frequent posters in this forum have positive things to say about the B. I trust them more than random people on sites like Trip Advisor.
Be sure to take a look of the following thread. You'll see opinions of people that have stayed at both hotels:
https://www.disboards.com/threads/best-disney-springs-hotel-with-best-price-transportaion.3644078/
