Quick edits: Snapseed
Photoshop Type Features: Photoforge2 (layer support, masking, curves, etc) and Photogene2 (clone stamp, retouching, etc)
The interface on Snapseed makes it super easy to get up and running fast. The others are more feature-filled but have a bigger learning curve, and are overkill for a lot of people.
Whatever you get, make sure it saves at the full resolution.