Is Bus from LiuLiQiao or DongZhiMen easier and faster to JinShanLing Great Wall?

You can take the bus from Dongzhimen station. After you get on the bus, you can tell the conductor that you will get down at Jinshanling. Then you can find many buses to reach the bottom of Jinshanling after you get off the bus. Taking them to reach there.
You still need to follow the same way back to Peking City. The last bus is around 19:00, so if you can reach the place you get off the bus, you can go back to Peking. The bus from Peking is around 85 RMB.
In my opinion, you had better take a one day tour so that they can driver you there. I used to take this tour https://www.travelchinaguide.com/package/beijing/jinshanling-hiking.htm from TravelChinaGuide, I think it is wonderful. One tour guide accompany me to finish my trip and they arrange the route according to my requirement.