You're still at the early stage of the game, I would recommend you to use team 7 still until 40+, get more ninjas and then set a new line up.

But me three stars are way better than team 7. and also how can I lvl up fast (besides bounties)

Bounties and dailies are what you can do for exp. 9tails too.
And I think what Narbsy meant is that Team 7 should work well enough to beat instance for now. Then, when you'll have more ninjas, that's when you should start thinking about which formation you're going to focus on.

What the guy above me said.

Attend nine-tail regularly, clear ninja exam as high as you can and sweep them, take 2 S-rank and 8 A-rank bounties and do dailies. Save your stamina potion for Monday because it's 2x instances exp.

Once you three-star your Sasuke and Hinata, you c*e them together as they all combo very well together. Last ninja can be either Karin for more chase or Kabuto which provide you extra clones to tank standards for you. Kabuto is relatively easy to farm from the exchange shop.

OOOOOHHHH thanks man

what formation for team 7
:D