The bed options are probably the main diff for my choice.
I have also read that if the busses are shared, then Swan is first for pickup (perhaps dropoff as well?) So, if the bus is FULL, Dolphin might get skipped? This is only what I've read somewhere, I have no experience. I had no big issues with the bus capacity when I was there.
The two are separated by a short walkway, BUT, if you are planning on using some service several times that is only at the one you are NOT staying at, that walk might get annoying.
A Possible Example: Using a refillable mug late night, if Picabu was the only place at whatever o'clock at night, but you're staying at Swan.
Just sayin - if you are going to be walking miles and miles in the parks all day, after a few days, walking over to Dolphin for Picabu might get you thinking about switching. BUT, you could probably get a room at Dolphin that might be just as long of a walk.
The pool "complex" appears to be closer to Dolphin (although Swan has it's own pool and hot tub that is not far away from the Dolphin's pool complex.)
Again, you could get a room at Dolphin, that is just as long of a walk as Swan.
Swan is also closer to the walkways to EP and HS, I think? But, it's really not by much.
I'd say the beds are the biggest difference.