I have
stayed at all three resorts multiple times, so can give you some personal experiences.
The rooms at all three are the same size. But...the BWI offers a deluxe room with a sitting area that is a bit larger than the standard rooms for not a whole lot more cost.
The rooms at the BC almost all have a full size day bed. The rooms at the YC often omit the daybed for a chair and ottoman. The rooms at the BWI usually have the daybed, but it's only about 4 1/2 feet long. All rooms at the BWI and YC have a full sized balcony. Some rooms at the BC only have a standing balcony. I prefer the decor of the BC rooms, the YC and BWI rooms are a bit "busy" with an almost dizzying floral wall paper.
The BC is the closet to walk to Epcot, the BW is the closest to walk to MGM.
The BC generally has the most kids.
The BC lobby usually bustles the most.
The BC has a great little cocktail lounge, it's tucked between the Cape May and the former Ariel's. We also like the Bellevue room at the BWI, although it can become overrun with kids. We're not big on the Crew's Cup at the YC, it's very busy with people waiting for tables at the YSH, and the lobby bar is often overrun with convention people.
In fact the YC lobby itself can become overrun with very noisy convention people.
When it's not busy, SAB at the YC/BC is wonderful. When it's busy it's crazy. The main pool at the BW can get busy, but not as. The quiet pool at the BWI is usually empty, same with the YC> The quiet pool at the BC isn't always so quiet.
All three have great restaurant options. YSH can be hit or miss, but is always at least good. YCG is a great, never crowded spot for a casual meal. Cape May Cafe has a character meal and an OK evening buffet. I haven't eaten at the Flying Fish at the BWI, but have yet to hear a negative review. There's a grab and go place in the store in the BC lobby. The Boardwalk Bakery is yummy, although lines can be outrageous, same for Beaches and Cream. One thing we've been doing is going to the cafeteria style place on teh ground floor of the Dolphin (sorry, can't recall the name) for breakfast, the prices are reasonable, and they serve Starbucks coffee with free refills during that meal. Blue Zoo is by far one of our favorite places to eat in the greater Orlando area--that's at the Dolphin. We haven't tried the new Italian place at teh Swan yet. Shula's at the Dolphin is a little too testosterone filled for us, but the meal was good. There's also ESPN and Big River for pub grub at the BW. So dining options abound. One thing to consider, if the weather is bad, you have to physically go outside when staying at the BW to get to any restaurant, at teh BC/YC it's all under cover, which is a nice feature when it's pouring out.
In my eperience, the BC has the most families, the BWI has the least number of families, the YC is inbetween.
All three have plenty of atmosphere. The YC lobby reminds me of the Waters Edge in CT near Groton. The BW lobby reminds me of what the great resorts of the NJ reosrt towns were back in the 1920's particularly in Ocean Grove and Asbury Park. The BC lobby is bright and "beachy" and reminds me of the Wequassett up on Cape Cod.
Bottom line you can't go wrong with any of them.
ETA: As far as views go, at these resorts, "water view" can include a view of the pool. If you book at the BWI, I'm pretty sure you can guarantee a Boardwalk View, which is nice if you like to watch the comings and goings. In my opinion, it's really not worth paying for an upgraded view at those resorts though. JMHO.
More ETA: There is plenty of excitement at all three of these resorts. First off all SAB is by far the most themed pool at WDW--CSR is argueably second. Next the Boardwalk area has various entertainment in the evening. Carnival style games, jugglers, musicians and more. You can rent surrey bikes and ride them around--those hills can get tough after a few adult beverages. You can rent watermice, take a pontoon boat fireworks cruise, or even a spin in Breathless.
