Unfortunately, the reality is that there are numerous cocksuckers to every cock. Every time I go out to one of the places around town which has gloryhole facilities, there are usually four to six cocksuckers for every cock. As soon as a guy wanting to get his cock sucked enters the appropriate cubicle, a complicated game unfolds which would make an ample field for sociological study, if it hasn't already.
If the guy wanting to get sucked is young, it's usually a case of the first cocksucker in. It doesn't matter whether he's overweight or not, for example. If he's over about 30, other factors come into play such as whether his cock is big or not, whether's he's cut or uncut, whether he's Caucasian or Asian, and so on.
The advantage of being totally promiscuous is that I always get to suck the cocks the others reject. I suck small ones, it doesn't matter much to me whether they're cut or uncut, and I never tend to look to find out what the guy actually looks like so most of the time I have no idea whether he's fat or what his ethnic origins are. All that matters is that his cock gets harder and harder and finally sprays the inside of my mouth with warm, salty juice.
BUT I admit I sometimes look out afterwards, just to find out whose cum I've just swallowed. Half the time the guy's nothing like I would have expected and that sheds a completely new light on the taste still lingering and tinging inside my dirty slut mouth. That's at least part of the reason why sucking cocks through gloryholes is so incredibly exciting.