Pretty sure Clerics make the best liches for the same reason Clerics make the best Necromancers- You have two domains and Rebuke Undead which can add bonuses to your powers over undeath. You can Bolster yourself. You can heal (Harm) yourself.
The wizard is no slouch either, and he'd have better damage-dealing ability, but the Cleric's going to have the edge here. Especially if we're only going Core.