The one vs. two piece debate continutes to be waged. Personally, I have used many of each and cannot find any real advantage of one over the other. If you are going with a tapered base, you will be using a one piece. I have also "heard" a theory that a one piece base will stiffen the action, potentially helping with accuracy, I have seen no proof of this though. Two piece bases are lighter.
As a side note, the US Army, on the M24, went from a one piece to a two piece base. I feel that as long as you buy quality, either one will work just as good as the other
MEL