scheduling backup_migrate with elysia cron
It all depends on your preferences and situation.

Elysia is designed to work in environment when you can trigger Elysia every minute (or every five, or ten minutes, but regularly 24/7). In that environment it would be more convenient to simply schedule Backup and Migrate with Elysia. Just remember to keep what you set in Home > Administration > Configuration > System > Backup and Migrate > Schedules in sync with what you set in Home > Administration > Configuration > System > Cron > Settings.

Benefit of that solution is easily accessible status of a cron task, the fact that you can see with GUI how long it took and when it was last fired, without login to any other tools but your Drupal.

Problem is that if cron system gets delayed, you may lost next sheduled backup - it may be mere 23h 58m since last time Elysia fired BaM task, so BaM may decide it's too soon to take another "everyday" backup. It's common problem with one scheduler calling another. And if you will make Elysia to trigger BaM every 5 minutes, to make sure everyday backup will be triggered consistently, you will waste a lot of CPU power for nothing.

drush bam approach is more direct. Long story short, it's main pros is lack of problems described above, and main cons is lack of benefits described above. And it's slightly faster in execution overall, as one "layer" less is in use.