Since you are going to be having your secondary talent spec set to Guardian, I would say feral is the way to go since the Feral gear is mostly Mastery based, which is good for tanks as well.
However, what I noticed from playing Feral is that it's VERY gear dependent and I could barely catch up with my peers playing in a top 50 ranked guild. You do have to put in double their effort to keep up. Probably not going to be topping meters in a while.
Balance on the other hand does well with low gear, and even better with higher gear. Shines in AOE and is all around the go to spec for dps.
Your choice will most likely be between what's more fun to you, compared to what's best for the group/raid/team/guild.
P.S. Cat Magic tower is lovely