Is it really a choice though? Easily Naruto Sage of Six Paths. Kakshi Susanoo, Tobirama Edo Tensei, and Hiruzen Edo Tensei are pretty decent support ninjas but if it takes you forever to save up for 20k coupons getting a "support" ninja is not worth the investment. (Since you are F2P or a low spender you probably dont have an insanely stacked pos1). AGK gets pretty hard countered by Edo Itachi (so if you dont see those that often, she might also be a decent choice.) Sasuke Rinne Sharingan is kinda fun to use but he requires a pretty decent supporting cast and is not as flexible as some other choices. Minato Edo Tensei I do have fun using but I mainly use him on my auto space time teams or ranked teams to make full use of his undodgeable mystery. If you want to use him in PvP, you gotta use someone who can steal chakra. Bee 8Tails chakra is overpriced, not worth 20k.

Naruto 6 paths is the best because he removes shields and buffs on chase while causing immobile, has a lot of different units that can buff his damage, has a mystery reset, and leeches. Without a doubt, he is the most annoying ninja to deal with currently with Edo Itachi being a close second.

To be honest, I rarely ever use Kisame with AGK. Plus, you'd have better luck using Kisame to stop Edo Itachi from using a mystery in the first place rather than actually clearing his debuff.

If you get no BP from saving up coupons because you are not investing those coupons into power....then you're definitely using the Sun and Moon shops incorrectly.