I've stayed at POP, POR, and Music. The buses for all of them are good. Movies sometimes shares with Sports/Music. Usually in the morning Movies has their own bus. But, I have to say that even if they don't share a bus, the lines can get long at park closing.
Same thing with POP. I found the bus system there to be fine. But it is a large resort, so the lines can get long first thing in the day, going to the parks..especially MK. And the lines at park closing are huge.
POR is also a large, spread-out resort. It has 4 stops of it's own, and then you add FQ bus stop, it could total 5 bus stops. I usually only used the main stop at POR. The lines didn't get too bad.
I would say that for the most part, the bus system works very well at most of the resorts. Some of the resorts, mostly the deluxes, have some little bus issues. Is there a particular issue or concern you have? I'm not sure I would change my resort based on the bus system. It could be terrific for me, but not work out well for you.