We've stayed at both, and it's really dependent on what you're looking for out of your vacation. We love both!
Beach Club:
-more bustling, and crowded...but lively and fun
-great for families, seemingly more children around
-KILLER pool! Enough said
-Multiple levels of dining (from counter-to fine dining) between the BC/YC complex
-only about 1/2 rooms have full balconies
-only about 1/2 rooms have daybeds
-views are hit-or-miss. there are some astounding views, and some really lousy views
-walk to Epcot is a cinch, DHS is a bit tricker as you have to take the boat, or you're in for a long walk, busses are no better or worse than Boardwalk
Boardwalk:
-Feels lively, but ultimately quieter
-feels more adult-oriented
-dining ranges from walk-up pizza window, to fine dining at Flying Fish (our favorite restaurant on property, tied with Narcoossees)
-pool is our second favorite after WDW and has the distinction of always feeling cool and refreshing, even in August!
-vast majority of rooms have full balconies (like 95%)
-vast majority of rooms have daybeds (like 95%)
-views are better overall, because the "cheap" views are of a lovely garden, or the front entrance, which I think is pretty. water views are amazing
-walk to Epcot is really only about 2 min longer than BC...if that...closest walk to DHS if you wish to walk....busses are similar to BC.
Hope this helps!