I would probably have to say the Vedder out of the three that you mentioned for winters on the fly. The Gold is a steep gradient river with lots of canyon water, and although there are some good spots, not the best fly fishing water. The Stamp can be awesome to fly fish when the water is lower, but as most will attest it is a massive flow in the winter. The Vedder is a good size and has lots of great fly water and open gravel bars.
Good luck,
BL