Annotable

Over at The Sweet Setup, Annotable was picked as the best iOS app for annoting images. It's easy to use, has tons of great tools, and makes it easy to sync images to other devices. It's a free app, and it has various options for upgrades for additional tools, colors, and styles. It also includes an app extension to edit directly from the Photos app.

You can read the entire review at The Sweet Setup. You can download Annotable for free on The App Store.