1) First of all judge the availability of yr Database i.e. whether it is 24x7 database. Also find out how much downtime can yr management take.
2) RMAN can take backups of databases both in Archivelogmode and non archivelog mode. Using RMAN you can forget about what was backed up and when. It stores everything in the control file or in a separate repository in a different datbase.
3) RMAN is capable of directly copying files onto the tape.
4) RMAN is able to do incremental backups. If using exports you can take incremental backups.