I've stayed at Yacht Club and Beach Club, but not the Boardwalk. The Boardwalk is slightly more convenient to Hollywood Studios (depending where your room is) if you are a walker. I find the layout of the YC/BC more appealing and more accessible to restaurants. It's a turn off to me that if you stay at the Boardwalk you have to walk out to the "street" to get to restaurants. I believe they have a coffee bar set up in the lobby though. I don't think either resort has a typical sit down breakfast at the moment (Captains Grille being remodeled and Trattoria Al Forno turning into a character breakfast), which for us is definitely a negative. The bar outside of Yachtsman's Steakhouse and Beaches and Cream are great casual options.
Stormalong Bay is lovely, however IMO it has an odd layout. To ride the main slide you have to walk across the path in your bathing suit - no thanks! The lazy river is nice, but tiny. If you have littles with you the sandy area can't be beat though. The hot tubs get full quickly. I think Boardwalk has bigger ones.
You really can't go wrong with either - walking to Epcot for dinner is the best!