Well, I favor the dry ice method as it is fat less time consuming. But there are trade-offs between the two methods.
Dry Ice will be faster, and give you a higher yield. But the resultant hash will generally be of lesser quality, especially if you use a larger micron bag and shake the crap out of it. Also I have found that if the humidity is high when you are making the hash, the screen can accumulate condensation and clog up. For these reasons I generally only make dry ice hash in the winter, when it is cold here in Michigan, and the humidity in my home is really low.
water hash will usually give you a smaller yield of higher quality. This will also take a lot more time and energy. If you invest in an automatic "washing machine" then this will obviously require less effort.