visiting the best part of the wall in Dec for a half day and with bullet train transport.

i will stay No.9 Shijia Hutong Chao Nei Nan Xiao Jie, Dongcheng. i have 2 days, i am planning for first day at the great wall, which part do you think it will be the best if i want to come back the tow by 3 or 4, by using the fastest transport way (gullets train)?

i am still young and i can fit hike up and down. is there any way to rent a bike and ride over the wall?

thanks
zaher