For DVDs - DVD Catalyst. No contest here. I have all the mainstream converters, and this one beats them hands down for DVD to Droid conversions.
For Blu-Ray - Pavtube Blu-Ray Ripper. Of the Blu-Ray rippers available, this is the best I've found so far. Audio/video sync is great, and they just released the instructions for making a Droid profile (optimal settings): How to employ optimal settings when converting videos to play on Motorola Droid?