The definitive is CAV, which means there is less video noise (The SNR is up to 3DB better than the CLV version), typically less crosstalk, and better image stability, and better colour stability. It also allows you to do slowmo and still frames if you are using almost any laserdisc player.
The NTSC transfer itself has some problems, split sabres on some frames, some edge jaggies on others and some 'trails' as a result of a 'virtual' dirt removing algorithm that didn't work so great.
Being CAV it is more discs, so more side changes to deal with, and some DEF editions had some missing footage.
The US faces set is CLV, so a little more video noise, image stability- especially edge stability is noticably worse (but can be fixed with an external TBC in most cases) and crosstalk is evident on most players.
It is a better transfer in some respects, no split sabres, better edges in some scenes, none of the dodgy trails, but introduces some artifacts of its own, e.g. beter colour in a lot ofd scenes, but worse colour stability and a noisier chroma signal. Being CLV there are less side changes to worry about.
The Japanese Faces set however seems to be the same transfer as the US definitive set (albeit with a different black level) as it also has the split sabre problems.
Some of the above issues may or may not be visible depending on the quality of the player you have.
The DEF edition also supposedly is more susceptible to rot, but both my DEF sets are rot free.
This is not the only differences by a long shot- but the ones that I care about at the moment.
That is why we are using both sets to create our master.