Hello, Elizabeth!
I love talking Walt Disney World® Resort accommodations! Disney does an amazing job of transporting guests to a variety of places just by stepping into the lobbies of their fabulous resort hotels. You've also selected my two favorites! Here is my advice on which location I think is best for a runDisney race weekend. And the winner is......
Disney's Yacht & Beach Club Resort!
Beach Club is my preferred resort of the two. I find the location of these Epcot Area Resorts to be extremely convenient when participating in a race. Not only are you in the heart of Walt Disney World® Resort, but this location is also very convenient to all race activities such as the runDisney Health & Fitness Expo and the race-morning Start Zone Area. You'll also have access to a multitude of dining options with Disney's BoardWalk Resort and the Swan & Dolphin Resorts just steps away. My favorite benefit of Disney's Yacht & Beach Club Resort, Stormalong Bay! This is the best resort pool area on property and my favorite place to relax post-race! These resorts are also host hotels for this royal race. So all your transportation needs will be provided.
However, it is worth mentioning
Disney's Polynesian Village Resort is my second favorite! And with construction from this resort's re-imagination scheduled to be completed in 2015, next year's Disney's Princess Half Marathon Weekend would be a great time to stay there (especially if you've been waiting on construction).
I hope this helps give you some help, Elizabeth! You have great taste in resorts! And please do not hesitate to reach out to me with any further questions as you begin planning and preparing.
Faith