Indeed, I have to vouch for ffmpeg as a the best solution. When I built GifMachine[0], it's pretty much just a web interface and automation layer to ffmpeg/imagemagick. Imagemagic and ffmpeg I found to be easy to use, fast, and delightfully scriptable. Using them together also produces the prettiest results.
For example, here's a gif produced with just ffmpeg: http://i.imgur.com/DWc4OdD.gif
And here is the version produced by ImageMagick: http://i.imgur.com/OdojPSo.gif
While the one made using ImageMagick looks better, it's also less compressed and takes up more space. So it's a tradeoff between the two.
[0] http://gifmachine.xwl.me/