If u dont have many ninjas go with team 7 (sasuke/naruto/sakura) you get free frags so ez to get them 2 star. Actually all ninjas are viable but not all work good together. There are some ninjas who work in almost every team: Hinata 2 star / Sasuke 2 star / Shikamaru 2 star / Kabuto from redemption shop 5 frags for 500 points / Neji 2 star. It depends on your main character which one you shoudl take but i recommend Sasuke 2 star with hinata 2 star since they add tons of combos (lighting attribut in general have good combos).

http://*.qq.com/tool/huoying/mnq.htm

With this site you can check out which passiv you should take its a teambuilder i think it is explained how to use it in the strategy section somewhere.