What about aluminium?
Still I'd love to have a classic-ish stainless steel bike with disc brakes.
Now I have a carbon road bike, don’t care about the weight, did care about comfort. Comfortable, flexible, but still has stiffness in the right direction (torsion is way less). Longer rides are much more pleasant.
There are also nice titanium bikes and steel bikes. From what I heard titanium and steel frames tend to be a bit more flexible, no idea why.
Yet many people will say carbon is more 'comfortable'. Its hard to tell how much placebo it is.
Of course it is a complicated system, so you can never compare it 1:1. Fact is that carbon bikes tend to ride more comfortable, if they are designed for it. Also the frame can be shaped and put together to flex in the right directions, which is harder with aluminium.
Then again, there are also endurance bikes (many 1000s of km's a week) made from titanium (J. Guillem) which are comfortable and also have much simpler shapes than carbon frames.