Many travelers choose to get to Lhasa from Hongkong as Hongkong itself is a major transportation hub and tourist desination. Among the routes to Tibet from Hongkong, travel to Tibet via Chengdu is the most recommended.
Sichuan Tibet overland Tour includes the Northern and Sourthern routes. Most people can't identify among the 2 routes. Check the overview of what you would be confronted with when you take either route and find the best one for you.