Today, you're probably better off with a single B.Net account.
Primarily for the B.Net bound items.
You need one authenticator per B.Net account, and have for quite some time.

If you have a single authenticator attached to several different B.Net/Warcraft accounts...
It can be advantageous to log in, with a single code for all accounts at once.
But the B.Net bound stuff is tempting too.
If you're a new account, this isn't an option... so the single B.Net makes a lot more sense.