I mostly agree with Kuro, but there are also somethings that I believe are different. First, I do believe they are different, though I would go as far as say they're nothing alike. They each serve their own purpose, but that doesn't mean they won't swap roles, so to speak. I also think that, although in the Judeo-Christian beliefs describe a Guardian Angel as a winged human who protects someone, I believe that that is only one branch of Guardian. It's entirely possible to have an Animal Guardian, which can serve the same role. Believeing only in the idea that Angels can only serve as Guardians, which I'm not saying they can't, limits your thinking to one specific idea, when it should be open to possibilites.