I once owned a Cognoscenti, and I liked the hit/playability of it. A friend has a Bluegrass that I've shot with several times and I slightly prefered the Cog. The Cog hits a little stiffer and harder. IMO, you won't go wrong with either one. They are both great cues.
With that said, I think you should also consider a Chudy. He, like Cognoscenti, uses the G-10 pin. Chudy's cues hit softer although they have a stiff shaft taper. I personally prefer my Chudy to the Cog I had and any of the several Bluegrass cues I have played with.