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A bit dated but here's comparison of these top tier (at the time - 2009) OSS platforms.
http://moo.nac.uci.edu/~hjm/UCI_OSS_Backup_Evaluation.html
And of course, trust none of the solutions offered in their backup mode; it's the restore that counts. Pay special attention to the format of the backup. Bacula uses a proprietary format, but includes all source for building a restore utility. Amanda uses only common archive formats; BackupPC uses semi-std formats. Commercial backup solutions often use opaque, proprietary formats so if you stop paying support, they own your backups.