Sea
I have it, haven't earned a gift card yet. It doesn't track steps as well as caskwalk (will miss up to half of them). It has longer ads, but you collect more coins between ads than cashwalk. It's looking like it will take a little less than twice as long to earn a gift card with it than with cashwalk. Which makes it the second best walking app for earning money that I've tried. (After cashwalk)