I tried at least five code snippet apps, including Dash, CodeBox, Snippets, and a few others. Quiver is the one I ended up buying. I find it to be excellent, and very well priced.
It has a few bugs, and a few missing features (which the developer told me he planned to implement, but that was over a year ago, so I won't hold my breath). The primary bug is that bothers me is that it does not maintain the window state between sessions. So the width of the sidebar reverts back to one that is not wide enough for my liking, each time I quit and start the app. There has been no update since June 2016, so I am starting to think this app may have been abandoned. That would be a pity, if it's true.
The feature I would like to see, which the developer said he was working on, is a better (more automated) way of capturing snippets from web pages, and of handling the pasting of code and text into a snippet. Ideally, such that pasting code and text will automatically break the content into text and code cells accordingly.
I highly recommend this app.