I think it depends on what parks you mostly want to visit. If it's Epcot and Hollywood Studios, then probably BC. If it's Magic Kingdom and Epcot, then Poly. If you just want to see all parks I lean towards Poly.
I agree with this. It all depends on which parks you will visit more and also how you want to spend your evenings. BC offers a TON more dining and recreation activities within walking distance than Poly does.
Poly - short monorail ride to MK, long monorail ride to EP, bus to AK and DHS
BC - walk right into EP (line is always shorter at the IG entrance, too!), boat to DHS, bus to AK and MK
I travel alone with DS5 a lot and for the past few trips, I have chosen EP resorts over MK resorts because I like to go back to the resort midday, swim or relax and then have the option to simply walk around the Boardwalk or back into EP at night without having to get on yet another bus or monorail. Plus, after Illuminations, you just walk right out and you are back at your resort - no more lines!!