Have stayed at both a lot of times. Keep in mind that when it comes to amenities, the resorts share their main pool/laundry. But it's a fairly quick walk across the breezeway from one property.
Bus transpiration to Ak/Mk is the same for both properties and shared with Swan Reserve (as is the laundry) and I believe SR guests can use the S/D pool but S/D guests cannot use the SR pool. Both are walkable/boat to DHS/Ep/Boardwalk which is our main reason for our stays since they're usually, not always, much more competitively priced than the Disney crescent lake properties.
Here's some general info off the top of my head, I'm sure I'm missing a few things.
Swan
Queen beds with heavenly beds
smaller resort than dolphin
No laundry room, located at Dolphin
more chill/refined laid back smaller lobby
QS is Java for AM coffee but not near as large/stocked as Fuel
Dolphin
full size beds-not sure of mattress brand
shape of hotel lends itself to long hallways if you're far from the elevator but keep in mind, it's interior hotel hallways so climate control is plus. but resort is a bit larger than Swan.
More upbeat/vibrant fun lobby with large central bar/hangout area but can be a negative if people prefer a quieter atmosphere
Fuel grab and go is a large QS with all day hours so makes grabbing food on your way in/out super convenient.