My expereience is that MS Exchange Admins are a dime adozen. I have a friend right now who chose MS Exchange and wishes he hadn't due to the flood of admins around him who compete for his position. It is funny how people will bad mouth you when you are not looking so that they can say they would do a better job than you. That just doesn't happen as much with NBU admins.
Also like the others have said you get a variety of OS's to work with.
Just my option!!
Less headaches and less on-call time :-)
For some reason most data owners want weekend full backups.
And if ever there is a 3 day weekend...yep you guessed it. They got to have both a full backup and a restore.
Yes, those events happen in the Exchange world but you would only be concerned with Exchange and not the 35 other servers with diverse applications running on them.
When your thinking of your career don't forget time with family. You might want to move that to the top position.
These words are spoken from the heart of a 50+ old man :-)