How to go Mutianyu Great Wall

1. Compare between Mutianyu tourist bus vs Dongzhimen Tourist Bus Line, which one is most convenient?
As I understand from your info , Mutianyu bus located near exit E of MRT Dongzhimen station while we need to walk a little to Dongzhimen bus station to transfer Dongzhimen Bus line. Do I understand correctly?
2. Both bus line are directly to Mutianyu great wall and ticket office, correct? No need to connect any...
3. Do both bus operate everyday or weekend only?
4. Do I need to reserve the ticket before arrival date? If yes how and where/ or It can be walk in at that day?