Here's the reply I got from a SQL Server MVP. He's the DBA at a large shop here in SLC.

Well not sure that MS has ever put out a Best practice of tape or file
before. I don't remember ever seeing them say one way or the other.
Personally being a DBA and what I've used the most is backuping up to
file. This gives the DBA the most flexibility over his backups it also
allows him to possibly leave 1-2 weeks or days or some sort of retention
amount on the disk before he needs to request to tape. This empowers
the DBA to deal with his own restores if needed.

Going the agent route I see this in a lot of shops that don't have a DBA
there network admin runs the SQL and he uses an agent to backup exchange
and then just uses the same agent to get SQL. I've seen these agents
cause problems for sql in the past but this could be human error more
than anything. I've also seen admin's that don't know there backup
software well or don't understand how to use there software with SQL so
they end up restoring more over the top of things or backing up at the
wrong time or things like this.

So what it comes down to is personal preference and need. Depending on
what you need and who will be there to manage it. I wouldn't call
either a best practice though because I don't think MS has ever said one
way or another.

>I don't agree, but I'm checking with a couple of SQL Server MVPs.