I am interested in making a Cleric/Mage and I currently have Cleric up to 20 and Mage up to 15.

I was going to switch back and forth as I level up keeping both classes around the same level… kind of a leapfrog method. After reading the forum a little bit and hearing all the problems regarding adventure ratings, I am unsure if this is actually the best method or not.

A.) Is it best to go up Mage first to 100, then add Cleric next?
B.) Is it best to go up Cleric first to 100, then add Mage next?
C.) Is it best to leap frog my way up switching back and forth?

Any advice would be greatly appreciated.