'ke chha' is Nepali famous and common sentence for 'Hi' :)

In general, "Namaste" is used all over the Nepal. However, "Tashi Delek" is used in mountain and hilly region. Likewise, "Jojolapa" is used by Newar ethnic group of Kathmandu valley.

Tashi Dilex

The common word that I used when greeting is "Namaste".