We have done 3 trips completely off-site and our last trip we did a combination of All Stars Music and off-site. On our next trip in November we are doing 2 nights at Pop Century then moving off-site for a week.
What I found with All Stars Music (we were in Rock Inn) was that it was a hike to the buses, the food court and the main swimming pool, even to the parking lot for our car. The room size was actually not too bad - I expected the Disney rooms to be smaller but they utilize the space well. We did use the bus system and it was okay but we did have to wait about 20 minutes for a bus.
What I love about off-site, you have laundry in your unit so you can pack less. You have the full kitchen so you can make snacks, reheat leftovers, have meals in the unit to save money, etc. I also love all the space with separate bedrooms, extra bathrooms, having a living room - it is so nice. Also, you park right outside your condo so only have to walk a few feet to get into your unit.
I found the swimming pools for off-site that I have stayed at to be nicer than the pool at All Stars. Off-site typically doesn't have lifeguards but Disney does.
What I liked about staying on-site was the Morning Wake Up calls with the gang singing was cute. The parking being included was nice and the Extra Magic Hours were great to have access to. When you stay off-site, if you avoid the Disney park with the morning EMH, then you will have the same advantage as any of the Disney guests as long as you are there at park opening.
I prefer off-site because I don't like waiting in lines and when you stay on-site, you are in lines for everything - food court, bus system, parks, etc. The entire vacation is spent waiting in lines and surrounded by people. With off-site, you have lots of space and flexibility. I don't find being off-site to be inconvenient at all - I think that time wise, having your own car and driving is just as fast as doing the Disney buses.
Have a wonderful trip.
