Since using the new version of Symantec, I've experienced lots of problems doing incremental backups of clients' SQL databases.
Is Windows Server backup a good alternative to Symantec Backup Exec 2012 for backing up SQL databases?
In my opinion, the best product for performing SQL backups is SQL Server itself. When space permits, I backup to local disk (full + differential, tx log backups every 10 minutes). These files can then be backed up by your third party software (to tape, NAS, etc.).
If I need to do an emergency restore (assuming a non-drive related issue), I already have the files local to the server, no need to mess around with restoring from tape or copying across a network.
One client of mine had used a third party software to backup files directly to tape (a proprietary format). Two years later they needed to do a restore (audit). They had a great deal of difficulty performing the restore because in the meantime they had upgraded the OS and the backup software, which no longer was compatible with the tapes they had from before.