Well, stream backup utilize the BEDS API into Exchange API for receiving a stream of data for the Information Store. This methods works fine for most installations. This does however put some load on the Exchange server instance.
Snapshot: First, snapshot backup is the only method for Exchange 2010. Snapshots can be useful if you have a large Exchange server, a,nd/or want to offload the data move by doing off-host backup.
NBU will initiate a snapshot of the Exchange Information Store, and Exchange will by using its VSS Writer, make sure the data is quisced and consistent. NBU will then make a file backup of the files in the snapshot. Once finished, NBU can release the snapshot. If you want to do off-host backup, you would need to either use Storage Foundation for Windows, and use mirroring to break off one mirror during backup, or use a VSS hardware provider, so that the SAN disk system takes care of the snapshot. Once the mirror/snapshot is ready, the volume is presented to the NBU media server, which then makes a file backup of the files.
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