Is anyone has some information on this matter, all the collectors i have go to see have the same items (most of the shiverpeaks and some of desert). So if someone has a clue...
Basically, the collectors have the same stuff with slight improvements as you move along in the game. So at one point you could get an Ascalon Bow with 2-8 dmg and later on you can get one with 13-22 dmg. There really isn't much variation between the types, however, you get some nicer upgrades as you progress.