The K Factory chassis is, even though it's 1mm thicker, 35 grams lighter than the stock chassis.
The CF sideguards are made in Switzerland by the way.

You can't really compare and choose between these materials, because each of them has their advantages and disadvantages. Titanium is stronger than aluminium, but also heavier. Carbon fiber is lighter, but it can break.

An all carbon fiber chassis would not be optimal since it does not absorb heat from the engine. Also, the car would be much too stiff and we've seen what happens if a car is too stiff. *cough* Thunder Tiger *cough*. And a carbon chassis would suffer a lot more from all the scratches from bottoming out than an alum one.