For us it's:
1-Fantastic CM's, they went above and beyond when my DD got sick our 1st day at WDW
2-location, location, location-resort design The resort is so easy to get around. We loved our Niue longhouse last time and felt that we were steps from everything. During our most recent YC stay, our room was very far from the lobby, pool and food. We had quite a trek every time we wanted to get anywhere at YC.
3- location, location, location of the Poly vs theme parks. It's so easy to hop on the monorail to get to MK. A quick walk to the TTC can get you to EPCOT quickly or take a bus to AK or DS. We like the bus service, even though it shares with GF and/or CR, it was quick and easy. At the YC this last summer, the buses were horrible. They did not come quickly and then the YC buses to to BC, Swan, Dolphin and BW before going to your destination. This added so much time and took so long, we ended up taking a cab several times.
4- Size of the rooms. We have two teens and space is important. Plus each room has a daybed. This helps our family a lot. We can request something else besides a daybed, as it's standard.
5-Theme. The Poly is gorgeous and themed so beautifully. We spend a lot of time exploring the resort and enjoying the GCH and lounges
6-Wishes! We do like Wishes, but do not enjoy the pushing and crowding to see Wishes at MK. At the Poly, we watched Wishes from the pool, the beach, the GCH and this time we will watch from the CL lounge.
7-Food options. The Poly has great eateries, but you can also take the monorail and eat at CR or GF. So many great places to eat on the monorail line.
8-We were there in 2010, so it's been a while but our room was spotless. We never saw any issues with carpeting, mousekeeping, GCH or the pool looking rundown. We had wonderful mousekeeping.
My only issues were our fridge did not keep items cold, even though we had the door open. I had read this was an issue, so we brought a collapsible cooler with us. And the main pool was super crowded. I hope they do start checking hotel card and wristbands, that would eliminate so many problems with the pool.