Rain is good because you can abuse Hurricane with Thundurus, Tornelos, and Dragonite. You also have stuff like Starmie, Sharpedo, and Azumarril to be strong Drizzle attackers as well.
Heck, 8 turn Rain Dance teams are still good because they get to abuse the ridiculous swift swimmers. Thundurus and Tornelos work great to set Rain up, and abuse it as well!
Hail isn't too impressive in my opinion, I really don't like it. Every single Hail team I fought I beat rather easily, but I could be wrong.
Milotic in Rain? It seems a bit too defensive for a Rain team unless you use Rain Stall, which happens to be pretty good since you can use stuff like Rain Dish Tentacruel and Blastoise.