SNAPSEED
The best by far. You can do so many things with the app. What I like about this is that, there are wide varieties of editing tools and filters you can choose from. This is the go to app that I use whenever I edit photos to make them look nicer.

 



VSCO
This is the first editing app that I used before I discovered Snapseed. There are some free presets which I think are pretty and you can just use them alone without even using the editing options. However, the editing tools or options in this app are very simple and easy to use.
What I like about this app is that it has a studio where you can all see the photos you have edited. You can also copy the edit you made on photo to the other.




PHOTOGRID
I mainly use this for its "Grid" tool. There are layouts that you can choose from. You adjust the ratio on how thick or thin you want the border/s to be. However, currently, I seldom put grid on my photos. Maybe that's just my taste now. No grid effect. ☺