I have used a lot of photo editing apps for the iPhone, and this is by far the best. It allows you to have complete control over the firing of your photo with its wide range of tools. And if you are serious about photography, you can upgrade it to give you even more options. The amount of tools and great interface make this app a must have for photography lovers.
MAL_379 about Polarr: Photo Filters & Editor, v2.9.0