I suggest using this team, which is known as the "queen/empress team"
where kurenai and karin are both attainable at the stores
http://oi66.tinypic.com/2uf4zdd.jpg

so upgrade your hinata

and i also recommend upgrading all of team 7 to 3 stars,
they are useful in ninja exams

ok, thank you very much I checked that few people upgraded kiba or choji. So to sum up it isnt worth to upgrade others ninja ? P.S : I forgot about Kankuro. I saw that sometimes people use Kankuro. This post was last edited by ad2***@wp.pl at 2016-7-29 02:09

well for now, i guess you c*e them for survival trials or ranked battle,
but later on when more ninjas come out, you'll rarely use them.

If you want to upgrade a few out of these ninjas, i personally would upgrade choji and ino.
choji can work as a tank and ino can be used for ninja exams

edit: yea, you can upgrade kankuro, his mystery becomes an area attack