Way back when my boys were teens we tried both resorts and they loved BCV best.
They liked SAB and spend a few hours there but they loved BCV quiet pool. Boardwalk doesn't have a quiet pool, only the clown pool which is always crowded. the quiet pool at BCV is very quiet, sometimes there might be 10 people but I have never seen it crowded like the other pools.
they also liked OKW turtle pond area because the pool is quiet and they get to have fun without worrying about bothering others, but you asked specificly for Epcot area.
And my youngest said to add that there are more young people hanging out at the quiet pool at BCV. He met a few kids that he wound up hanging around with for most of the trip.
As to getting to the parks, the walk from BCV to Epcot is very easy, maybe 5-10 minutes. It takes longer going through security than it does to walk there from BCV. The walk to Epcot from BWV is also easy, just a bit longer, maybe 3 minutes. I never bothered with the boats from either because I was able to walk faster than the boat, and it was never at the dock when I got there anyhow.
The walk to DS is a bit longer for either resort, maybe 20 min at the most, but it is an enjoyable walk. I don't do the walk when it is in the 100's thought, I will do enough walking in the parks, so I hop the boat. Again, I walk faster than it takes the boat but on hot days sometimes you have to do what you have to do.