It depends what types you're good with. Rayquaza is the lead Pokemon in my party. I can use Outrage without him going confused, and his moves are really strong. Sceptile has good leaf blade and he knows a Fly type move, so he's good for me. Carry one Pokemon that knows all the Water HMs. I try and carry all types with me for any battle. Try and keep your party to have at least one move per type.
~Tikal