What's the best photo editing app for the iPhone?

Prefureably free and I want it to be able to remove acne and stuff

You'd be better using a computer and a proper image editor, such as Paint.NET http://www.getpaint.net or GIMP http://www.gimp.org/...w.gimp.org - both are free.

Just transfer the image from the phone to your computer open up the photo in the image editor of your choice - in GIMP use the healing tool, or in Paint.NET use the clone stamp tool.