Hobbit Gandalf is amazing in Secrecy decks. Especially once you have Arwen by his side, you have a 4 willpower quester who can then serve as a sentinel defender for 5. In Secrecy decks where most of your heroes (and many of your allies) are squishy, this is essential for dealing with more powerful enemies. As everyone else has mentioned, which Gandalf is better really depends on the deck. I don't think I've ever used Hobbit Gandalf in a deck with more than one Tactics hero, for example. The fact that both versions are powerful, yet very different from each other is a testament to excellent design.
In addition to Word of Command, another combo to mention is that Hobbit Gandalf is amazing with A Very Good Tale. You can commit him to the quest and still add his 5 cost to your total for that card. This makes it much easier to field expensive allies like Gildor, Faramir and (my favorite) Core Set Beorn.
Edited by danpoage, 19 May 2014 - 10:26 AM.