I think a sorc is prob better if you are going to solo because of the large amount of spells he can cast. A mage is best used in a party because he can be kept at the back and cast supporting spells.
As for the level ten spells you can check them out here:
http://www.gamebanshee.com/baldursga...gelevelten.php
By the time you get to level 10 spells you will know what is good to get. Improved Alarcy is good for massive rapid casting(like casting 10 magic missles all at once). Dragon's Breath is good for massive damage.