What are your interests - history, religion, nature, food, etc, etc? Do you want to spend all of your time only in Tel-Aviv and Jerusalem ? They are not good bases for seeing the Galilee & Golan and the Negev. Are you considering renting a car ? A car is a liability in Jerusalem and Tel-Aviv because of the parking and traffic problems, but it is highly recommended for touring the north and south. For the Galilee and Golan, I recommend booking a place for at least three nights in Rosh Pina, Kfar Blum or similar.