PicLab is a simple but well-designed and very easy-to-use image editing tool.
You can take a photo with the built-in camera or use one of your own. The app's layout makes it incredibly easy to edit the image. Chose from filters, frames, text or editing options (saturation, contrast, blur, exposure etc). No lag or errors, it just does what it is supposed to - and well.
While other photo editors may have more features, the ease of use and flawless execution make this one stand out.