Look at it like this:
You have Jiraiya, Orochimaru, Tsunade.
Toad, Snake, Slug.
Snake beats toad, toad beats slug, slug beats snake.
Now, Naruto, Sasuke, Sakura
Wind, Fire, ____
Fire beats wind, wind beats ____, and ____ beats fire.
Well, wind beats lightning, and water beats fire. However, Tsunade has an affinity for earth, and possibly water (Remember, her grandpa was the first, famous for the wood element, which is water + earth).
Taking all of that, my bets go to earth and water. Primarily water, due to water's significance as a purifying/restorative substance, and also in part to the fact that Sakura has been touted to surpass Tsunade (primarily in a medical regard).
So, in short:
Naruto - Wind main, lightning secondary
Sasuke - Fire main, lightning secondary
Sakura - Water main, earth secondary