We use both open top containers, ala plastic milk crates and covered ones, depending on the items. The crate type is just to keep items from rattling around, e.g. bg sprays, BBQ equipment, hoses, exterior shade screens, etc., while the enclosed ones are for gear that needs protection or are not so often used. Stackable containers are good unless you are getting ones so tall that there is no need to stack.
The right kind are the kind that fits in your bays and holds the stuff you carry with you. That will probably change as your your RVing style develops, so don't agonize too much over it.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL