I need fenders. I couldnt' find anything in Carbon that was made for fenders, so i went with steel.
Even though the major airplane manufacturer that i work with is making airplanes out of carbon fiber, i still feel more comfortable with steel. It's heavier, but it's a great ride.
Titanium, i hear, rides like Aluminum, but is lighter. it's also more expensive.
Aluminum makes some nice bikes too.