[r_smart]

I would argue that it is worse. If you are on someone's back, in a rear naked choke your entire body is set to controlling the person you're choking and you are defenseless against other attacks. Not just attacks from behind; you can be looking right at the second person and be in the position of having to decide whether to let the choke go to cover yourself or to stay committed to the choke. Worse, since the person you're choking has their hands free, you usually need to bury your face to keep them from doing things like gouging your eyes out, meaning you limit your vision. This obviously gets worse if you've pulled somebody into the guard.

Additionally, if someone is coming from behind, your ability to react is much faster if you're not wrapped around somebody else, giving you a better chance of protecting yourself.

*edit to add eye gouging into the equation.