You have listed two of my favorite resorts!
Both have something special to offer in terms of theming, location and transportation options.
Personally, I love the Epcot resort area. Getting on and off the boat that transports you to Epcot or MGM is a breeze with a stroller (if you're bringing one) OR you could walk to either parks, you are that close.
Then you have the Boardwalk at your backdoor for something different to do, and the Yacht & Beach Club are a stone's throw away.
As much as I adored the WL, everytime we were at Epcot, I would glance over at the Dolphin and wish I was staying there, I'd think to myself, look how close we are and I'm not staying there!
The WL really takes you away from the hustle and bustle of the busy parks, and with a little one, you might be looking for that.
Sheesh! I don't know what to tell you! Both are great choices!