Gandalf, without a doubt, is the most splash-able hero released to date. He can pay for any card (made easy with his Pipe), give you card draw, resource acceleration, and shadow cancellation with his Staff, and his willpower, attack, and defense allow him to fulfill any role a deck may lack, and do it extremely well at that!
With the upcoming release of Shadowfax, he will become even more splash-able and powerful allowing him to function better in multiplayer (giving him ranged and sentinel in addition to whatever awesome effect it may have).
Glofindel may have low threat, but he is nowhere near as versatile as the Grey Wizard.
Not to mention our future Narya attachment! I hope it has an incredible ability.