I would vote for Grandstand and Springs as the Best areas with Congress Park as the third best. Here is why:
Grandstand: 1st bus stop for all but DTD so if the bus is packed you got your seat (except in our family we give up our seats for elderly, pregnant women, etc, so I guess it's no biggie,

)
Has a nice pool of it's own, with splash area for kids, plus mug refill station.
Has an alternative walking path to DTD West that people often forget about that is pretty short (10-15 minutes leisure pace)
Not far from main area (Pool, Food) - 5 minutes or so
(This is the only place we've stayed)
The Springs:
Near all of the main activities and still fairly close to that walking path to DTD West.
Congress Park:
DTD Marketplace path is near by, but we actually like DTD West because we go to HOB nightly for outdoor entertainment and drinks after a day in the parks. We happen to love HOB and think it's a hidden treasure at DTD.
The views over at Congress Park of DTD are pretty cool.
Those are my picks! If we can't get a THV for our next trip, we'll try a request for The Springs I think.