Here are a few of my favorites so far. I do all my editing in phone--I really like some of the default filters the phone has, and I also use PicSay Pro (hands-down my favorite photo-editing app since I got my original Droid back in 2009) and Little Photo (I don't use this one nearly as much, but I use it occasionally.)
In-phone filters: high contrast+cinnamon
In-phone filter: Auto-enhance
PicSay Pro
PicSay Pro
PicSay Pro
PicSay Pro
Little Photo
which one is you