Welcome to iMore! There are a ton of good photo editing apps out there. I use [URL="https://itunes.apple.com/us/app/enlight/id930026670?mt=8&at=10l3Vy]Enlight[/URL].
For photoshop and other editing, I recommend these:
Leonardo Photo Editor
Superimpose
Handy Photo
Facetune
For enhancement edits, Adobe Photoshop Lightroom is great. I haven't had it long and every time I use it I'm going, "Wow!".