With the huge variety of image editors available for iOS, I find myself using Annotable more with every new update. Pixelmator and OmniGraffle are amazing pieces of software on iOS but for simple edits they are just too much work. With all of the tools unlocked (a $10 IAP) Annotable can blur, highlight, draw shapes and lines, as well as add text and very nice magnifier effects to any image. A recent update for Annotable added the option to adjust magnification for annotations, which I never even knew I needed.
The only thing Annotable doesn't do for me is resize images. Until that's available I use a very simple Workflow script that resizes proportionally to 400 pixels wide.
Annotable | Universal iOS | Free and $10 to unlock all tools