For modern RHEL you are recommended to use the systemctl command as summarised here: [recent] RHEL distributions should use the new systemctl command to issue poweroff/reboot. As stated in the manpages of reboot and shutdown they are "a legacy command available for compatibility only.".
However, if you use many different distributions, or distributions of various vintages, then perhaps stick with
shutdown -r now 'reason for shutdown'.
The main reason to use
reboot would be to avoid the risk of forgetting to add the -r when using
shutdown -r on a remote machine, which could easily result in not being able to login again and having to use the remote admin (if available) to restart the machine.