After selecting the LTS-Kernel during installation, I found out later that it is not used by default. (you can check with: "uname -a")
If you want Antergos to boot the LTS-Kernel by default, you have to edit the following file:
There are two ways to make grub boot the LTS-Kernel
First method: modify the following entry
You have to change the Zero, it marks the first entry in the Grub Menu. The second entry below is "1", the third "2", and so forth. (I had to fill in the "2")
The second method: Uncomment the following entry
edit GRUB_DEFAULT from 0 to "saved" that in conjunction with GRUB_SAVEDEFAULT will set the default to your last selection
Simply remove the "#" and save. This will force Grub to use your last selected Kernel as default - until you change it again.
Unfortunately, none of these methods is working out of the box, because Antergos is using a submenu in Grub after installation.
Hence you have to install grub-customizer from the AUR to get rid of the submenu. Its a GUI-tool, pretty self-explanatory. ! But keep in mind that this tool is dangerous too, it can make the system unbootable !
After that, both aforementioned methods work again.
This is a rather unfortunate situation.
My suggestion for the devs: Make the LTS kernel the default, if this kernel is selected during installation (ask the user eventually if he wants it).
Get rid of the submenu, keep things simple, list all the kernel options without Grub-submenus. I dont think that it would be to messy to offer four options during boot (Kernel, LTS and the fallback options).