Well, the likelihood of either happening is very low indeed, and the likelihood of one vs the other happening is neither predictable nor apt to be a function of who the defender is.
Well, lets see. Gang activity is pretty much unheard of in my corner of the world and I've never heard of anyone being attacked by more than two people in the entire 10+ years I've lived here. I also make a point of not frequenting "risky" places like bars where large numbers of judgement-impaired individuals are likely to be found. Because of these facts, I can safely say that I'm among those at lowest risk to face one of these nightmarish multiple-attacker scenarios that are always brought up.
I do, however, know from personal experience that most criminals are cowards and bullies and thus greatly prefer victims that are smaller, weaker, or at some other disadvantage to them rather than a fair fight. Because of this and the fact that I'm a fairly large individual myself (6'4" and 300+lbs) I would feel fairly confident in thinking that while I'm probably among the least likely to be attacked in the first place, should I have to actually use a gun in self-defense it would likely be against an attacker that is at least roughly equal in size to me, if not substantially larger.
I also know that part of my chosen low-risk lifestyle is to avoid confrontation and simply leave the situation if possible. Because of this, it is not an unreasonable conclusion that should I have to use a gun to defend myself, it will most likely be at very short range up to and including contact distance because, if the threat were at greater distance, I would attempt to retreat.
So, while it is true that neither situation can be predicted with absolute certainty, the odds of one or the other for a given person certainly aren't 50/50. Who the defender is, where he or she lives, and what type of lifestyle he or she chooses can certainly tell us which scenario is the more likely. It seems to me that when one considers multiple equally bad situations that might need to be faced, it is the most prudent to choose the tools that most adequately prepares you for the most likely of those bad situations.