kushina bt

Kushina is better, but Choji is way easier to get. There's nothing preventing you from building them both up at the same time since Choji you can get in the ninja collection using Survival points and Kushina you'll need to piece from events or spend coupons. The currencies don't overlap. You will likely get BT GNW Choji before you get BT Kushina, so why not just work on both and use Choji while you're finishing Kushina?