Nichi is a free app with paid purchases. I have the monthly subscription and I think it's totally worth it—it has a lot of really cool templates, stickers, frames and filters. I use it for covers, Instagram stories, and wallpapers! It's super cute and easy to use.
It allows you to save templates, so if you make one thing, you can keep using the same layout. It also has plenty of premade templates to use, and a plethora of stickers and frames and backgrounds.
I use this app the most out of anything else! I definitely recommend checking it out.