I've stayed at the Dolphin and most of the mods, and I like the Dolphin the best. The rooms are much nicer than the mods. It feels like a nice hotel whereas the mods feel like motels to me. Although, I wish the bathrooms were bigger and more updated at the Dolphin.
The reasons why we don't stay at the Dolphin, and we now stay at CSR, are purely logistical. I have a 5 year old, and we like having Magical Express (no car seats), we like the dining plan (we go during free dining), we like not sharing a bus with other resorts (at CSR), and we like having bus service to the front of Epcot, which is my son's favorite park.
If it were just me and my husband, I would pick the Swan or Dolphin over any mod.