I would recommend leaving it as a cron job. The only difference would be that you'd be putting some form of infinite loop in the script itself, which has no benefit other than higher time resolution, i.e. you can run it more than once a minute. If it crashes or hangs though, you won't know and it won't do anything. If it's a cron job it starts every minute, 30 minutes etc, so the logic is much easier and more reliable.
there is nothing magical about a "service"... it's just whatever you want it to be.