You can design Ti bikes to be as stiff as you like. I remember top (ex) pro Robert Millar having a custom Ti bike made for him for a Pro Cycling magazine road bike test. His specification was basically that he wanted the bike to be as stiff as the stiffest Aluminium bikes available at the time. He got what he wanted ...
My Cannondale is a very stiff Al bike and I really like it. If I stomp hard on the pedals, the bike takes off like a scalded cat. I make it comfortable enough to ride by using lower tyre pressures to take some of the sting out of rough road surfaces.
My Basso is made from oversized steel tubing so it is stiffer than most steel frames, but I still flex it when putting a lot of power through the pedals. I can get the chain to rub against the front mech. and I don't like that.
I always quite fancied a Ti road bike but I'd probably go for the Robert Millar approach and go for extra stiffness.
I'd like to try a CF bike some time to see what I think. If ithe magic combination of light weight, extreme stiffness
and comfort is possible, then I'd certainly be interested in that. The only thing putting me off is CF's catastrophic failure mode. My bikes get the odd knock and scrape but they still last me 10 years or more. I don't like the idea of my bike frame exploding a year after I scraped it against a cafe wall!