Screenflow 2.0 came out earlier this week, so I now have production copies of it and Camtasia:mac. I hadn't planned to do a head-to-head, but the opportunity arose today, so I took it. Below you'll find copies of the same screencast I did to introduce Summon to our community. The first was done in Screenflow, the second in Camtasia:mac. Overall verdict? Tie. Screenflow got 1 point because it had easy mouse focus (dimming the background), but Camtasia's Smart Focus, while it needed a little tweaking, made the zooms easier to throw in. Had I spent a few extra minutes I could've made the timing on the Camtasia zooms a little more uniform. I understand Screenflow has a few audio extra features, but I didn't do anything with audio processing for this one. Both were really quite simple to edit, chop out dead space, and add the closing text. I don't think you'll go wrong with either one.
Screenflow did do a better job with the automatic upload to YouTube; it asked if I wanted to upload as HD, while Camtasia didn't, and the result with Camtasia's upload was quite a bit fuzzier. I went back and used Camtasia's advanced export feature to export at 1024x720 H264, then uploaded manually to YouTub and the results were much better. I also didn't do an equal job on the cropping and zooming, so they won't be identical in dimension.
Incidentally, I also ran across this collection of links on the Screenflow blog of other reviews of Screenflow, including some comparisons with Camtasia.