Reflect is the better one (IMO)... then you have lots of combinations (Refl + wp, Refl + Draco meteor, Refl + Sandstorm, Refl + Rain dance) depending where you gonna exp it or duel (Brick break as Grayfoxx said)
My own dragonite has Reflect and Sandstorm, and for me it was the better option, you can easily exp it anywhere