My task was pretty straightforward: I had a group of processes that need to start in a certain order, restart if they die, run as a non-root user, and write logs somewhere. I needed to support RHEL 5, 6, and 7, which all use different init systems (sysvinit, upstart, and systemd). I worked with all of them and also experimented with alternatives (runit, s6, Supervisor).
For my task systemd was a pleasure to work with compared to the others. There was a bit of a learning curve, but once I mapped out what I needed to do the solution was obvious.
I found upstart to be almost good, but the version that ships with RHEL 6 is lacking compared to the later versions that came with Ubuntu. The Python-based Supervisor was surprisingly good. I sort of saw why some people might like s6, but runit's charm was lost on me.
sysvinit was by far the worst. I wound up using sysvinit to hand off to Supervisor in order to not spend my life worrying about the number of forks and pidfile locations.
I can't speak to systemd's shortcomings and perceived hegemony in other areas, but when it comes to acting like an init system it is miles ahead of everything else.