I just recently bought a 05 F150 FX4 and was wanting to level it out to make the stance look better. I know Ford's come with keys already, but don't know whether to buy a leveling kit instead. Any advice?

 

As far as I know, keys are on the torsion bar trucks. Buying a set to level out the trucks with bars was a waste of money if you ask me. There is a bolt on each key that you can turn to crank the bars, and get your lift. Rides like a brick, but you get your lift.
Leveling kit sits on top of the strut, changing the geometry of the front suspension, giving you your lift that way. Also hurts the ride a tad.
Good thing is, it's a cheap/easy way to add bigger tires. I have a 2.5" level on my 07, and am able to run 325/60/18s. It comes with a price though. I have replaced all the front end components after 55k miles of having the level on. I'm not saying it's 100% because of the level, but I know it doesn't help.