I screenshot every day. Although I got other tools like Cloudapp, Capto, or even the native Mac app, Markup Hero is the handiest one for screenshot annotation. It can also blur sensitive information you don't want to share with others.
Two things I love above others:
1) You can upload and annotate on PDF also
2) The blur function I mentioned before.

I would love to see:
- The option to dd or customize more colors
- Different types of lines (like a dotted or dashed line)
- Highlight function
- Scrolling screenshot (saw that it's coming for the Chrome extension, would love to see also for the desktop app since I don't use Chrome that often. Or maybe you can release an extension for Safari?)

It would be also nice to see if the desktop app can work offline, so I could replace totally my native app
when working offline.