We just did 2 adults and an 8 year old at ASMusic and it was OK, but tight. If the Q murphy bed is "down" there is barely any walking space and the chairs aren't useful for sitting as we had to stack them. If the bed is "up" then there are two hard, straight chairs to sit in. Either way, although it was OK sharing with a kid, I'd not have liked it if we were 4 adults.
Choices depend on budget and relationships (gender, friends or family, who is willing to share a bed, etc.) What we actually did was DH, me, and the 8yo in one room and DD/SIL in a connecting room. This gave us more overall space and two bathrooms (and two coffee makers and two fridges), and the little guy was free to "play" between the two rooms. Other "budget" options are ASMu family suites or family suites at AoA (but these are all double beds). Standard rooms at moderate resorts are larger, but not a whole lot. Then you move on to either studios or one or two bedroom suites/villas, either thru Disney directly or by renting DVC points. Either way, cha-ching, on our budget. We stayed at BWV one time in a studio that slept 4- a Q bed and a D sofa bed- and it was tight with 3 of us. The room we stayed in at the Poly last summer said we'd have 2Q beds but we ended up with a Q and a Q sofa-bed. UGH. The space was large enough for 4 adults, but who would get to sleep on the sofa bed (and we paid $400 a night and that was WITH a BounceBack 35% discount). SO... budget and relationships will be the defining factors.