This team, today? It would be either Suggs or Reed. Need a playmaker on defense in the worst possible way.
For me:
Ngata really didn't have as much impact as some of these guys, and wasn't an elite pass rusher
McAllister I personally felt was never that great of a Corner. Pretty good, but I don't think another Corner solves the major issues on this team.
A lot of people would probably say Ogden, but this is a top 5 offense in the league even with the Olineman we have, so I'm not sure he's like a gigantic difference maker.
Basically leaves you with Ray, Ed and Suggs. I wouldn't take Ray because, while he was a pretty good coverage linebacker in his prime, I really just don't think inside linebackers have nearly as much impact on the game today as they did when he was around.
If I had to choose between Ed and Suggs, in today's game, it would probably be Suggs. In his prime he was an elite of the elite pass rusher, and he was a high end run stopper. We don't really have somebody who can do both on this team, and our issues with pass rush are well documented. Reed is tempting, because we seemingly don't have a ball-hawking playmaker in the defense right now, BUT, I also think teams just wouldn't throw deep on him and attack the perimeter and underneath.