If you have lots of money the Cervelo P3 carbon is the best. Then the P3 aluminum 2nd. The P2K and Dual are ok. Cervelos have the best aerodynamics in the bike world. But the aerodynamics of the Kestrel Talon is good enough. And the Kestrel is one of the more affordable bikes if you're going to build from a frameset.
I have both the Cervelo Soloist Team (aluminum) and the Kestrel Talon. My Cervelo pictured weighed 17.4 lbs while my Kestrel weighs 19.03 lbs. My Cervelo is all Dura Ace 9 with 7800 brakes while my Kestrel is all Ultegra 9 with 6600 brakes. I don't notice much of a difference in my rides, but the geometry of my Kestrel fits me better. I guess I have to put a 60mm stem on my Cervelo. Both of these bikes are very fast, but I love my Kestrel the most because it has a Flightdeck computer and a Polar Power Output kit. My Cervelo is my ultimate racing bike though, but I'd really like it to have dimpled Zipp 404 tubular wheels. I hit similar top speeds on both bikes.
My Cervelo cost $3271.25 while my Kestrel with Speedplay Zero Ti pedals cost $3697.5
The one thing that you'll notice about the Talon is that...it has a shorter chain stay...thus you may feel an instantanious response when you accelerate.It will feel very aero and stiff.