We have done both, make sure that $500 is inclusive of all the fess they like to hide at the Dolphin. I know sometimes when we have looked there before, it looks like a good deal until we get to the "pay now" page, and it ends up being the same or more than some of Disney's Deluxe resorts. From our perspective, the last trip to either resort was pre-pandemic, and our daughter was 8, they both have pros and cons.
The quick Service at Pop is better, more options, fresher, and easier to get.
Transportation (for us) was better at pop, dedicated buses was a huge thing. and now with the Skyliner, takes away some of the benefits of Swolphin.
Pop is an actual Disney resort, so it just is a little better integrated, you can still use Magical Express until the end of this year for free.
Pop has lots of pools with a main "fun" pool, but you have to pay extra to be close-ish to the main areas.
Dolphin is nicer, the lobby, the beds (even though not as nice as most high end Marriott hotels).
It isn't Disney, so you get more of a feeling of a traditional hotel.
There was a while before it closed that the Swolphin wasn't served by Disney buses, and when you went to MK you got dropped off at the TTC vs in front of the MK. While riding the mono-rail is fun, and isn't that huge of deal, it adds time to your day.
Most of the time if you are a marriot card holder you get free upgrades.
Both have small beds, which suck.
Both are not the friendliest design, POP is spread out, the Dolphin has different towers and walking in and out of the hotel to get to the parks isn't exactly easy.
Both now charge for parking, POP is cheaper.
Both are served by Skyliner.
For us, when we went with a kid that young, we always preferred to rent a 1 bedroom DVC unit, or at Bonnett Creek's wyndham timeshare. Once the napping stopped we started to stay at the "normal" hotels.
