Do they like to swim? If so, Beach/Yacht Club have the best pool. I'd choose Beach over Yacht.
As far as being close to Magic Kingdom, you really can't go wrong with any of the monorail resorts. Our current favorite is the Grand Floridian. If you are going in the summer, they have tons of daily activities for kids at the resort. We used to love the Poly, but this was pre all of the construction. I haven't been back since 2013, so can't recommend what it's like now. I will say it's super easy to get to Epcot from the Poly bc you walk to the TTC and then hop on the monorail to Epcot. If you are going and all construction is going to be completed at the Poly, I bet your boys would love it. I would avoid Wilderness Lodge because it's going to have major construction beginning in the fall.