My favorite support would have to be Levy!
Levy is a very intelligent and also cute character, she will do anything to help out a person she cares for. I love the way she reacts when she is around Gajeel.
Two of my favorite scenes involving her is in the Tartaros Arc when Gajeel was nearly out of air due to the black water, and she swims to him and gives him the rest of her air. And in the Alvarez Empire Arc when Gajeel is getting sucked into the Magical Barrier Particle vortex, and Levy runs and try to save him, knowing that she could possibly die from doing so.
Also, did I mention that my favorite ship is GaLe? I think those two are so cute together!