I did visit both Danba and Litang. I liked both. Danba is in a steep-sided valley and the area's rather picturesque. Townspeople were very friendly; the villagers, less so. Did a couple of shorter walks to/in nearby villages. One with some watch towers and one where they were having a little horse festival - and most of the women were in traditional dress.Spent a day in Litang. It's much higher and the surrounding land is nearly all grass. Not as pretty IMO, but I've read a number of people extolling the virtues of the surrounding countryside. The main street is reminiscent of the Wild West, but the cowboys have motor bikes rather than horses. And beware the Sichuan chicken - never had anything hotter - and I don't mind eating chillies.
OMer Montgomery Wick has spent quite a bit of time in china, you can read about some of his bicycle tours in China here. They are quite funny at times and give an insight into china, I don't know if any are in the same area but well worth a read anyhow.
Forgot to say: only trekking I did was in the Meili Snow Mountain range in Yunnan. Did a little three day walk on the east side of the range. Very attractive area, but for the rubbish left by other visitors. There were no roads in the valley right next to the peaks, but it seemed there was mobile phone reception almost everywhere. Probably six or seven places to stay in this valley, so don't need to camp if you don't want to.
In Litang, only looked around the town & its immediate environs. Didn't go out into the hills (but did pass thru some of them going in & out on the bus).