As Dym has said unless you are a pretty decent spender I would * with power even if you are a low spender just power. You will get a lot of good ninja just from treasures especially now with edo treasure you can make the meta mei 1010 mabui team for next to nothing now, same thing if you exchange frags can make the meta light blitz team. Both of these teams are extremely strong and you will find most spenders medium to high still run these teams as they are just so strong (I am talking servers at about 6 months of age possibly older ones). As a medium spender who has focused a lot on ninja collection I would suggest just to go power, those super rare ninja may be shiny but a lot of them are no better than common ninja in this current meta. Is harder to beat a power gap than a ninja gap.