Most Windows Oracle Shops usually go the Windows Scheduler route. However, I'll list the 3 main ways that Oracle RMAN backups can be scheduled, so that you can make a decision what is best for your environment.
1) Oracle Enterprise Manager (via Enterprise => Job) which you can read all about from the docs.
Keeps all of your backup control in a centralized location. This can be a pretty big deal if you have many Oracle Databases to manage their backups for.
Creates a dependency between OEM and all of your backups. If OEM goes down, your backups don't run for any database. This may not be as big of a deal if you keep your Recovery Catalog in the OEM database, since if that is the case for you, the dependency is already there (unless you have a failover to perform the backup using the Control File if the Backup Script can't talk to the Recovery Catalog).
No external dependency (provided the backup scripts are local). Automatic logging of runs for reporting.
Running desktop executables from Oracle can be a little tricky. You either have to start the OracleJobScheduler service, which is deprecated as of 11g, or create dbms_scheduler credentials, then attach those credentials to the scheduler job, which Tim Hall explains here. No centralized maintenance or reporting (unless you schedule them from the same machine, but you may create unnecessary dependencies there).
3) Windows Scheduler
Easy to setup and maintain.
No centralized maintenance or reporting (unless you schedule them from the same machine, but you may create unnecessary dependencies there).