Krissi, he's soooooo cute! Got to agree though the jumping one looks best. More likely to get a response from that one I would have thought. They can see what he's capable of.
I would use the third, its a really cute picture. The rider in the jumping one looks a little tall and its not the best jump in the world he looks a bit untidy, but I don't suppose that matters really for a kids pony.
Its always good to have a jumping one but I'd try and get a better one personally