I would say Aldon Smith first, in then Phil Taylor. Aldon Smith would be a tremendous OLB across from Hali. I also like Phil Taylor to be the NT of the future. He's the type of guy that can collapse the pocket, preventing the QB from stepping up and getting Tamba and Studebaker more sacks!
I'm not too fond of the other guys. Pouncey is nowhere near his brother's level, and that's where a lot of the hype is. Titus Young is climbing up boards, but I like Jon Baldwin better as a deep threat and he should be available at 21 also.