IS has the strongest heals. But KF healing is good too - especially with Bliss the Muse Your biggest threat will be anti-healing, especially from FW - Skull of Decay relic, so make sure to include Seism to destroy that relic if it appears. Cleanse for Decay will also be important. You will need things to prevent power turns/one-rounding of your champs in order to benefit from healing.
Healing Builds don't really work since most of the builds around here function on champ removal. You can't heal was has just been killed. You'll have to combo it with something that prevents champ removal like Protection. As for healing, Rejuvenation Rings are the boss healers, and Aspect of Life after 10 rounds are the best healers in the game.
How very DARE you! Griefbearer’s Fountain is delicious young man. 32 initial heal plus contest. Get a dwarf onto the case for 32 heal every turn.
It's been a suuuuuper long time since I played but as I recall Elven Wizards can get some decent healing going. With Chains of Amareth you get extra HP for your guys, Elven Illusionist helps to increase the healing from Elven Statue, and though not a Wizard, Elven Page works well with Mena and comes with global heal.