I find GrabUp (http://grabup.com/) better than Skitch, mainly because I never use the extra features that Skitch gives on top of just taking a screenshot and uploading it.
Skitch adds annotations and sharing with almost the same simplicity as the built-in keystrokes. I typically use "⌘-Shift-4, Space" as well, when using the screens in my own work, but not when annotating or sharing.
For quick annotations, pointing things out, highlighting things, and instantly pasting someone a viewable image URL (with one click to capture, and one click to share), Skitch is tough to beat.
I find a combination of the native key shortcuts with Dropbox works for me (you can also get a viewable image URL if you drop it in your Public folder.)