I almost didn't bother with this post after running a quick Google search on Jing vs Skitch and finding nearly 1,000 results, but I went through a fair number and couldn't find anything that actually compared them side by side, so I went ahead.
Both Jing and Skitch are free (currently) programs for Mac OS X that allow the user to take and then annotate a static screen shot. But they each do a whole lot more as well. Here's a chart comparing some of the features of each:
|Send to Bluetooth||X|
|Send to Printer||X|
|Attach to Email||X|
|File Format Outputs|
|iSight Capture (still)||X|
|Erase and Cut||X|
|Resize after capture||X|
|Drag snapshot into application||X|
So on options, Skitch is the clear winner, but that ability to record quick video with Jing is a damn good reason to keep it around. Plus it's important to note that I'm kind comparing apples and oranges here, as Jing never set out to be an all-inclusive screen capture product.
There's another important thing to consider too, and something a table can't capture (ha!) is the usability of each product. You know I can't resist a quick screencast, so here's how I use each one: