I've been watching Ward and I'm sold on him as a legit NFL safety. He is very solid in coverage, and despite almost never being in the box is always around the play. He's a playmaker and a sure tackler who takes good angles.
Watching Bucannon it really isn't close to me, Bucannon hits but he over-pursues and is not much in coverage.
Ward may not have elite size, but he is about the same size as Ed Reed and Troy Polamalu. There aren't any Kam Chancellor/Sean Taylor sized guys worthy of taking high.
If the Pats want to target a safety later in the draft that is fine. I'd prefer they address other positions early, but if they are going to get one in the first two rounds I'd make it Ward, as it sounds like Dix and Pryor are going to be gone by then. I may prefer Ward to either of them anyway, I'm tending to agree with Manx that he's a very good player.