16 days beijing/shanghai/xian what's the best place between?

Hi, as for your case, it is suggested to visit the representative old architectures in these cities and other scenic spots, temples in their suburb areas. Here is the information I know:
Beijing: Forbidden City, Temple of Heaven and Summer Palace cannot be missed. Besides, Jingdong Karst Caves in Pinggu District and Miyun Reservior base in Miyun District (you can enjoy yourself by bicycling).

SH: Apart from the attractions in the city, such as Yuyuan Garden, Jade Buddha Temple, Xintiandi and Temple of God. You can take high-speed train to nearby Hangzhou and Suzhou to have a visit. Hangzhou is famous for West Lake and you can travel by free bike; The water towns in Suzhou, such as Tongli and Zhouzhuang, as well as the Classical Gardens are must see destinations.

Xian: It is an ancient city iyself, so you can see many ancient attractions in the city, such as ancient City Wall, Bell Tower, Drum Tower and Big Wild Goose Pagoda. Besides, Terracotta Warriors and Horses cannot be missed. Famen Temple in Baoji city, and Longmen Grottoes in Luoyang are also suggested for you.

For the destinations travel between cities, high-speed trains should be the best way.

Thanks Samel for your Reply :) ...May God Bless You

I like to spend summer vacation in shanghai,I want to be sure where I can meet foreigners and more Chinese people speaking English,Beijing,shanghai,Guangzhou or wuhan?

Hi, you will meet more English-speaking foreign people in Beijing, Shanghai and Guangzhou.