As far as ranked battle rewards, I think it's current rating, not current league.

And to anyone else who might be reading comments and considering vcdragon's bots, I think the ROI on a new alt account is questionable. My experience is about a 30% win rate with just a few added cards, so they struggle to get out of bronze 3 on their own. And with the changes in bronze rewards, they don't earn a lot from loot chests. It requires significant investment in terms of buying and/or renting cards to get them to "earn" well. I don't know where that breakeven point is. More than I wanted to invest in an alt account.