I like /etc/crontab. It is a simple text file. Nothing magic. Standard. Works every time. Well known by everybody. Works on a lot of UNIXes, old Linux systems etc.
I don't want no new complexity and a new way to do things every 6 months. What I hate most is that all this is pushed through our throats no matter what we want. FFS.
EDIT: BTW, I think luckily, /etc/crontab at least currently still works on Ubuntu Server 16.04 (what I've tried). I think this is the way to go. If you want to use some new features (systemd) you can opt-in. But don't break old stuff please.