Hi there! In my opinion, go and pull in the Five Kage Treasure for now, because almost all of ninjas in that treasure can help you with your early-missions to level up. You c*so get the barrier ninjas there that you'll need in some battles, like Darui and Danzo if you're a Lightning, Mei for Water, Kazekage Gaara if you're a Wind or Earth and so on and so forth. I find GNW treasure great too but almost all ninjas there are suitable for higher-level players as it is contains ninjas that has some purely strategic gameplays. Try to draw in Jinchuriki Treasure I too and get Roshi, he is one of the most versatile ninjas in the game and can be used in the long run, draw in this treasure after you get your desired barrier ninja and some ninjas good to pair with the barrier ninja.