distruction and restoration is the 2 magic skills thats takes a long time to upgrade.
mystacisim,alteration,illusion,alchemy,and congeration are easy to upgrade if you wanna lvl fast atleast choose 1 of them.
I actually don't like to lvl fast,I feel I get more out of each lvl when I don't train on major skills...just the way I like to play.
Just remember the higher lvl you are the harder the game is not easier.
But yes very easy lvling if you use that method.