I've stayed at AS Music 3 times, and will be going to our 2nd trip to POP this December (during Pop Warner week). I'm a Value resorts girls and I don't care who knows it!
I really liked ASMu, having stayed there 3 times (seems like more...?). I think my DH picked it for our first trip since it had to be a value for our budget and I love Music however it's a great choice. it doesn't usually attract the sports groups that sports does, and it has fewer kids than Movies (Movies has more recognizable icons). We stayed in a Preferred room 2 of 3 times, and that made our experience 1000000x better. The preferred rooms are in Calypso, which is right next to the food court/lobby.bus stop and right by the main pool. The other time we were in Rock N Roll which was SO far from the bus stop and after a long day of touring that 15 minute walk seemed to take hours and I think I literally broke down into tears..but enough with how pathetic I am.
Last time we stayed at POP, which I really liked. The rooms are pretty much exactly the same as the All Stars. The square footage and amenities are identical except (and please correct me if this has changed) that at the ALl stars they have shower gel and shampoo (no conditioner! gasp!) in an inshower dispenser, wheras at Pop you get a bar of soap and shampoo bottles.
I like Pop a bit better, for one, it's novel to me. I did stay at ASMu enough for it to be "home", but it's also newer and shows less wear. The lobby is beautiful. i really like it! The theming is very interesting. I think the best thing about it is the layout. Instead of being like a long T shape, the buildings are mosre clustered around the lobby, so you can only be so far from the buses. We stayed in the 70's building and I didn't feel like I was walking miles to the bus stop. It's also closer to Epcot (the All stars are closest to AK), and you do not share a bus. We found that most times at the All Stars we did share a bus. It was mainly at park closing that we did not.
Pop also has a different food court layout. The all Stars have a separate food court and gift shop, wheras Pop has one large open area. It's kind of interesting.
I'm excited to go back and explore it and see how it's decorated for the holidays. We're seen ASMu decorated for the holidays i think all 3x we were there, at least partially because it was either Dec or early Jan that we were there and I like the music theme. I'm sure Pop will also be lovely.