Just to clarify - are you comparing a
DVC studio to a
standard room in a Deluxe Resort, or a DVC stuido to a
Deluxe Room category, in a Dluxe Resort? There is a booking category of Deluxe Room at BWI, BC, YC & WL (possibly at others but I've never looked into them)...that category is a MUCH larger room, but it also costs a lot more, and they are all Club Level. These rooms all have 2 queens plus a daybed or sofa bed, guaranteed. They have a lot of space in them, plenty for a pack-n-play.
I'm thinking you mean a standard room in a Deluxe Resort. I think the only standards in Deluxes that guarantee the daybed are Poly & CR - in the others it might only be a request. Someone chime in if there are others.
I've stayed in a studio, in a standard room at a Deluxe, and in a Deluxe Room at a Deluxe. If cost is not an option definitely go for the Deluxe Room, or even a 1BR villas as others have suggested. A studio is going to be tight with the pack-n-play, and everyone will have to be quiet all in the same room if the baby is sleeping. A standard Deluxe room without a daybed will also be tight.
If you go with Poly request one of the longhouses with larger standard rooms, I know Tokelau is one of them. They have extra floor space which is nice.