Quite simply, this is the best tool I have found for this job. It is the easiest to use, processes files fast, and has a nice interface.
I've tried many, many tools for video conversion in the past. They all had their ups and downs -- the worst of the worst being inconsistent output -- but I had finally settled on Avi2Demux for a long time. But that particular app had become unstable on Mac, so I had resorted to using it on my Linux box, or firing up Parallels to use the Windows build.
Now I can finally dump Avi2Demux altogether, as this app does the job and does it even better. If you are going to convert videos on even a semi-irregular basis, this is well worth the $8. (Yes, it is based on ffmpeg, so there are free alternatives out there that use the same thing, but ffmpeg can be a complicated beast, and this app takes all the guesswork out of harnessing the power of ffmpeg.)