If you want really long-term durability, titanium would be the way to go. Carbon fiber, after all, is just a high-tech fiberglass-type material, and like fiberglass, it can shatter, though modern frames don't do that too often. If you've watched bike races on TV, you've seen what disasters can happen to carbon-fiber wheels in a wreck. It's great for pros like Lance who can get new bikes or wheels whenever they need them. I'm just not sure I'd want to invest in it again long-term. My previous bike was carbon fiber and it is now a dinosaur because it was only 7-speed on the rear and can't be resized to 8-speed, 9-speed or 10-speed. I've gone back to steel, but if I had the $$ I would get titanium. If the industry decides to move to 11- or 12-speed (heaven forbid!) a titanium frame could be resized to acommodate the wider spacing.