It really depends on what you are looking for to make in the end. Dragonscale is supposed to be pretty good for a AGI/Crit specced Hunter because of the attack power bonuses and such. Each of them have their strengths and weaknesses. Check out this thread for more info: http://wow.allakhazam.com/forum.html?forum=69;mid=1131559767260411772;num=7;page=1 -- about halfway down is a brief description of the branches and a link to even more info about them.
In short it really depends on what you are looking for to make and what you want to have to farm for the items.
And when you read this post: http://wow.allakhazam.com/forum.html?forum=69;mid=114018319940456456;num=2;page=1 you will see that I obviously have no Idea what I am talking about. But Ancalimanarion makes a pretty succinct and simple summary about the three trees of Leatherworking.
Edited, Wed Feb 22 10:29:46 2006 by Broaddus