Does the Inglesina Quid2 fits in all airline overhead bin, and which would you recommend for traveling to different countries, the Quid2 or the Libelle 2?
The answer depends on multiple factors. The Quid2 was already taken on board as cabin luggage - multiple moms I know had it so. It, however, is a tad on the taller side, and some strict airlines might have a problem with it. It is vital to check with your airline of choice and their exact requirements, especially on the measurements they allow. 1-2 centimeters difference should not really make a difference, but 8 to 10 could.
About the Quid vs. Libelle, this again depends. First, on your child size and capabilities. The Quid lies flat, so is better for smaller babies, however has a smaller seat (so it will last shorter) and is larger after folding. The New Libelle from Cybex is smaller and more practical for traveling, however it is better for a larger/taller kid as it doesn't recline fully and is on the simpler side.