I guess you mean best transcoding/compression for best image quality...
Then hands down, it's DVDRebuilder using Procoder2 as encoder. Not cheap, and very slow.
Using HCenc as encoder, as Kerry proposes, will be slightly faster, slightly lesser in quality, and free (included with the free version of DVDRebuilder).
Next in quality is DVDShrink, with "Advanced analysis" activated and "Maximum Smoothness" compression option. Other settings are not as good. Will be Faster than DVDRebuilder/HCenc. That's what I use and I'm perfectly happy with it. When movies ask for too much compression, I burn to DL media.
Then there's all the rest, which looks significantly inferior to my eyes, while perfectly acceptable to most.