I used both Instagram and Snapseed. There are other Apps on the smartphones to do simliar stuff like Hipstamatic, but I ignored those.
Snapseed is a full featured image manipulation tool for your phone. You can straighten, crop to any size, adjust contrast, brightness, add grain, etc.
You can share the pictures to Facebook, Twitter, and other Social Media places. It integrates with them well. It doesn’t have its own social media aspect. It’s a pure image manipulation tool.
Instagram has multiple, preset filters to choose from. It is part of its own social media group where you can follow other Instgramers. It integrates with Facebook and other social media okay. It only offers one size for cropping: a square crop. It’s a simple tool to share photos.
Which Do I Choose?
I like Instagram better. Snapseed has a lot more features and tools, but why would I need that for my crappy camera phone?
In the end, I like the social aspect of Instagram. I also like its presets instead of trying to recreate it by scratch with Snapseed. Just press a button instead of fiddling with it for 5 minutes. I do think Instagram needs the straightening tool though.