There are a few things to take into consideration that may help you decide on which hide to purchase. First being the type of hide you would like. I bring this up, because if you decide that you want to try your hand in aging the jacket, then the choice of leather should be taken into account. Lambskin would be the easiest to distress, followed by cow. Goat and horsehide you would have to put a lot more effort in to get the desired results.
Now the distressing part isn't very difficult to do either. Just depends on how weathered you want it to look. A simple soaking in water (knock off the shine) and then allowing it to partially dry and then wearing it till it finishes drying will allow it to form to your body and allow the sleeves to crease. If you wished to further age the jacket, you could use rubbing alcohol or acetone. Be sure to test the effects of these on a inconspicuous area to see if thats the look you want. You could also use a scotch brite pad or fine grit sandpaper to hit areas where a lot of natural wear would occur. ie: elbows, shoulder blades, bottom of cuffs.(When doing this kind of work, less is more.) There are a lot of different tutorials or people who could help you out with this on other forums. Filmjackets has a section on distressing jackets and so does ClubObiWan.
As for the pre-distressed hides, they offer more a generic "aged" look. Reminds me of jackets from the late 80's. And I don't recommend using this type of leather as a base to distress further. They tend to look funny. At least I haven't seen one done properly, outside of the ones Tony Nowak made. But other than that, its a great hide if you just want something thats different from a plain dark brown leather jacket.
So now you just have to decide what you would prefer to wear. Its obvious which category I fall into. I just like the idea that I can age my jacket to make it look the way I want. But to each his own. Take some time and look around at your options before making your decision and I believe you'll be more happy with your purchase. Good Luck