/*
* This question isn't about diminishing other operating systems !
* I'm just have no idea. 😫
*/

Is there a big difference on the amount of packages on pacman, apt-get and yum. Can I use either of them and be sure that most applications are available ?

There are more packages that I needed that were not available in apt than in pacman. Aaaand of course there's the AUR. But probably that's just my subjective opinion.

(Pacman ships header files in the normal package which I find quite nice. On apt I always have to install 2 packages)

@b3b3 Then I'm ready to test out some arch-based distros.

For me personally the AUR is easier to use than ppas. Every package I ever wanted was very easy to get via pacman + an AUR helper while I had some problems with apt.