Added after 9 minutes
Personally, I like to level: Summoning magic (a vital skill for mages... specifically the phoenix rules and elementals are pretty strong), Education (a skill that strengthens a mage by 1.5 times), Sorcery (the mage becomes uncontrollable, especially ORA—casts 3 times while the enemy hero takes their turn), Luck (I love it when the phoenix deals double damage to enemy shooters :) , and it helps Archmages too - they don't have a long-range combat penalty and hit everyone in sight). And finally, you can take Logistics or Light magic (resurrection is a good way to minimize losses in battle)