I have never ridden a titanium bike but from all I have read basically the reason they feel responsive or "nice" is because they are so expensive they have other upper level stuff on them like good carbon wheels and high end groupsets to make it feel super nice. However the "modulus" or flexibility/stiffness and ability to work with is very similar to aluminum so blind fold yourself, put a high end groupset and fancy carbon wheels on a 500-1000 dollar Aluminum frame you won't feel a difference vs similar Titanium. The only difference is Ti is a bit less susceptible to corrosion and lasts longer but the "forever bike" or "forever X" is silly because the truth is with technology you are denying yourself access to new and better bikes that will eventually be far better than anything you could dream of currently if you keep the same thing for decades. And no Titanium is not repairable either so once you bend it or break it in a crash it's done just like Aluminum. With something so inexpensive (relatively, compared to say motorcycles or cars) why not upgrade at least every 10 years? So the point of Ti is very limited.

But carbon? It's what dreams are made of. Stiff, fast, ultra responsive and yet they can make it compliant in other ways so it soaks up the bumps: stiff when you pedal, soft when you hit things, carbon is what dreams are made of. If you never tried a carbon bike, you truly are depriving yourself, get carbon!