Difference between Systemctl and service command

service operates on the files in /etc/init.d and was used in conjunction with the old init system. systemctl operates on the files in /lib/systemd. If there is a file for your service in /lib/systemd it will use that first and if not it will fall back to the file in /etc/init.d.Also If you are using OS like ubuntu-14.04 only service command will be available.

So if systemctl is available ,it will be better to use it

With borrowing from this answer:

service is an "high-level" command used for start, restart, stop and statusservices in different Unixes and Linuxes. Depending on the"lower-level" service manager, service redirects on differentbinaries.

For example, on CentOS 7 it redirects to systemctl, while on CentOS 6it directly called the relative /etc/init.d script. On the otherhand, in older Ubuntu releases it redirects to upstart.

service is adequate for basic service management, while directlycalling systemctl give greater control options.

Moreover, systemctl runs services file from this path: /lib/systemd/

Service started as a helper script for sysvinit an latter became a wrapper script that works regardless of having sysvinit or systemd.