I can only give recommendation on what I have ridden in the past and what I am currently riding now. Past - Cannondale 3.0 frame ('86). Very stiff feel most rode anomolies, but still a good ride. After about 15 yrs on that bike I've gotten 2 new ones. Both Cervelo's (P2K and R2.5) The P2K is alu. with carbon fork and carbon seat post. Smoother ride than I had on the Cannondale. Very stiff frame, I feel as if every ounce of stength is going into forward motion. R2.5 all carbon (butted frame) feels like riding on melted butter to me, as in soft. Frame still is very stiff but it feels like your riding on good roads most of the time. I like them both. For most rides though I take the R2.5 but that is also because it's a road frame not a tt/tri frame. I would recommend getting carbon if possible. Very nice.