Aluminium bike or not?

Ride quality (whether compliant or stiff) has more to do with frame design than material choice. But carbon is the most versatile material for creating different ride qualities. You can design a super-light, super-stiff, aero race bike (which is why ALL pro race bikes are now carbon) or a far more comfortable compliant endurance bike and everything in-between. Metal frames are more limited in their scope for design and aluminium frames in particular tend to have the least compliant (harshest) ride feel. Some people simply prefer the classic looks of a steel or Ti frame and enjoy the natural ride qualities of those frames. Carbon frames vary massively in their feel from one bike to the next, so it’s harder to characterise them in the same way. Something like a Specialized Roubaix is going to feel very different to a Pinarello Dogma or Colnago C64. My own carbon road bike (Giant Defy) is very compliant and comfortable and yet stiff in all the right places when putting down the power. With aluminium there would have to be more of a compromise in the design. For example you might achieve the same stiffness, but for a higher weight and less compliant ride.

If your budget allows, I would try a few carbon bikes and see how you get on. With your Focus Paralane, you have a good solid baseline to compare. As others have mentioned, steel and titanium are other valid choices for your next bike.