I'd say for f2p, best ninja would be Han.(as a starter)

Han removes buffs and shields, so he evens the playing field since many p2ps and p2ws are running root or heavy shields.

To properly utilize Kushina, you would need HUGE health or she'll die.

You will need to be able to keep her alive and unless her health is somewhere 25k+, dont.

Go for Han and J.Minato over Kushina tbh.

Going for J.Minato or MM would be great.

MM is a great support ninja.