I made that question myself and I just read all the official webpages.
I personally liked it Runit and S6, runit is simpler and it just do what it has to do and it does it well. But in my opinion people should give a chance to S6, it's amazing and it's very fast. Of course the final decision is yours.
If you want to change Connman for Networkmanager you only have to remove connman.
pacman -R connman connman-<theinitiyouchoose>
And install Networkmanager:
pacman -R networkmanager networkmanager-<theinitiyouchoose>
For example, if you choose runit it would be like this:
pacman -R connman connman-runit
pacman -R networkmanager networkmanager-runit
When you uninstall Connman you also have to be sure that directories "/var/lib/connman/" and "/var/lib/connman-vpn/" are gone otherwise you might have problem with Networkmanager.