I love Snapseed for the initial cropping and subtle enhancing but I find the filters and effects quite limited so I tend to move onto something else after that.
I have been looking for another free app to use in my courses that will fill this gap. At the moment I think Pixlr Express by Autodesk is the one although Adobe Photoshop Express is a possibility too. My concern about Pixlr Express is that this current version is a little buggy. Sometimes I load a picture and it shows nothing and sometimes it crashes on a save but it does have some nice effects. I manipulated this butterfly picture using the adjustment>stylize>watercolor option and then applied a border:
It's useful to know that Autodesk also have an online version and a free Windows or Mac App that you can upgrade to Pro.
The app becoming my absolute favourite is iColorama (sorry, I know I keep on mentioning it but it is just awesome). By the way make sure you download the right version. When I was watching some tutorials online I couldn't understand why the features were different and then discovered that I was using the iPhone version (iColorama S) on the iPad and the iPad version has a little more so needless to say I have bought both!
I therefore couldn't resist trying out some of the options in iColorama I haven't looked at yet. Here are two results:
I got this by going to Style>Edges and then putting a mask using the Brush Mask on the butterflies and flower to make them come through.
The next one was a big surprise and I got it by going to Form>Tiles and trying one of the tile options:
