Virginia Tech and the FBRI have different user directories and email systems. Virginia Tech email addresses end in @vt.edu and FBRI (and VTCSOM) email addresses end in @vtc.vt.edu.
Which is preferred? That's up to you.
If you are FBRI Faculty or Staff, most every interaction with you will take place through your FBRI, firstname.lastname@example.org, email address. If you will be participating and using FBRI email lists, shared calendars, free/busy scheduling, and want visibility to the address book, you will want to use your @vtc.vt.edu mailbox as your primary account. People on the main campus, as well as systems such as payroll, will notify you using your @vt.edu account. To avoid confusion and manage your mail from only one account, click here to learn how to forward your Virginia Tech mail to FBRI.
If you are a student, it may make the most sense to continue to use your @vt.edu email address as your primary account.