I think the repeater is more useful than the threepeater, since it's cheaper and it shoots two peas in its row. Although at the beginning the threepeater may seem more useful since it covers more lanes, not only is that usefulness cancelled out by the expensive cost of the threepeater, but also by the fact that it becomes useless long-term, since later the repeaters provide a lot more firepower by shooting twice in their own lane, while the threepeaters shoot only once in 3 lanes.
OK, so I head news of a new S.T.A.L.K.E.R. addon - Call of Pripyat. I was a big S.T.A.L.K.E.R. fan and played both the original and Clear Sky. Clear Sky had all the things a proper addon required: better graphics, gameplay, faction wars, etc. But now I'm wondering where S.T.A.L.K.E.R. can go. I saw the several screenshots posted of it, and the graphics look exatly the same as Clear Sky (which was already imperfect by the time Clear Sky came out), so we know the graphics didn't change. I doubt the gameplay could change in any way, since it was pretty much the same in the two previous games (though the faction wars did make Clear Sky a great deal more fun) and the hunt for artifacts will probably be like Clear Sky (though they could make the anomalies look nicer). Sure, there will be new locations and according to screenshots NPCs can use knives now, but I doubt that will drag Call of Pripyat out as a full-time addon. As a result, I doubt it will be a success, but I hope GSC will make a good job of it.