I think that Togepi would be a good choice. As mentioned in it's Ruby/Sapphire entry:
Now Which Pokemon would be the best for competing with you in a three legged race? (i.e. the pokemon whose leg will be tied to yours)?
As its energy, TOGEPI uses the positive emotions of compassion and pleasure exuded by people and POKéMON. This POKéMON stores up feelings of happiness inside its shell, then shares them with others.
Now Which Pokemon would be the best for competing with you in a three legged race? (i.e. the pokemon whose leg will be tied to yours)?