Looking to go to Benasque without having to rent a car so likely bus from either Madrid, Pamplona or other towns that I can connect from if it's easier. I may be coming from San Sebastian direction.
Either from Madrid, Pamplona or San Sebastian, you have tto go to Huesca and conect to benasque by a local bus. You can find the time table from Huesca to Benasque at www.alosa.es
You can reach Huesca from Madrid by train. It is a high speed train, expensive and not many frequencies you can check at www.renfe.es
If you want to go by bus, I think that you have to go to Zaragoza (check www.alsa.es) and conect to Huesca (www.alosa.es)
Pamplona is closer, but I am not sure if there is any direct bus to Huesca or you have to connect at Jaca (www.alosa.es) about 8 years ago