Why not Dragonite? It learns Aqua Tail and in case you need it Hurricane.
Mmm i dont know, i tried dragonite and didnt like it
Hmm, he would have been the ideal option with Multiscale, Thunder, and Hurricane, but to each his own.
Latios works best I think. He resists anyone who wants to abuse the rain with Thunder and can support with an increased strength Surf. Salamence is a prime Pokemon, but I usually run Fire Blast on him, which is useless in the rain.