Phone Photography

The answer depends on what you are after:

I use Photoshop Express for photo editing, it has tools to touch up photos if there are blemishes or objects in them that you want to edit out, plus a whole host of sliders and filters to enhance or alter the look of photos. If you want a quick "boost" to your image if they look "dull" the auto option works well too.

Perfectly clear is a simpler app designed to automatically enhance photos, making them look punchier and more pleasing. Photoshop (or Lightroom as Ryan had suggested) can do all of that too, but the interface in Perfectly Clear is simpler and easier to use for quick enhancements.

After Focus allows you t blur out backgrounds, which can make for more attractive photos of people or close-ups - many modern phones already have a mode built-in that does this, but After Focus can help to touch up the effect if your phone didn't quite get the blur right or add the effect to phones that don't provide the feature.

Adding the last one just for fun as it's not really for editing, but "Storyboard" by Google can take your videos and photos and turn them into comic strips, which can be a fun way of sharing a series of photos with people!