Backup Software

No simple answer to this one.

It depends on:

The type of backup device you plan to use;
The backup strategy you plan to use;
The size of the database you need to backup;

Efficiency is also a relative term based on your requirements.

A simple, no frills, cheap (i.e. free) solution is the NTBackup utility built into Win2K/Win Server 2003. The downsides to this software are that you can't do a brick-level (i.e. mailbox-by-mailbox) backup, if that is a requirement. There is also no support for tape libraries, nor is there support for backup to CD/DVD, if those are functions you are interested in.

For other software, make sure it is either exchange-aware right out of the box (not usually the case), or can be made exchange aware through add-ins. This is a critical capability. Changes entered in Exchange transaction logs are only committed to the information store when a full, online backup is conducted. Any other type of backup causes the transaction logs to continue to accumulate. Only backup that is Exchange-aware can conduct online backups.

Dedicated enterprise-level backup software, such as CA Brightstore and Veritas BackupExec provide many more bells and whistles/options (sometimes to the point of being difficult to configure correctly). Both of these require add-ins to become Exchange aware.

I would personally recommend Veritas Backup Exec with the Exchange Agent - I run 7 Exchange Servers supporting 4000 people and I swear by it.
Its easy to use, setup and configure - and it also very easy to restore with.

Look at CommVault. We switched from BackupExec to CommVault because of its ability out of the box to support Exchange Mailboxex as well as the rest of our enterprise.

I can finally sleep weekends not monitor BackupExec throughout and entire backup cycle.