Doesn't really matter what class you are. Anything goes. There are so many NPC's, that you'll get a balanced party with any class of choice. For "the best to complete" (ie most powerful), i'd say the only thing would be to have atleast some fighter in your class. Either single, dual or multi.
Same for weapon profs. All proficiencies have their good weapons. But long sword is a good choice, since none of the NPCs use that by default. Or flail. Or spear. Or, or, or. There are so many weapons in the game, that it doesn't really matter. Just go for what you'd think'd be cool.