Ancalagon
Dusty Dragon
I would think the warlocks are not tied to the guild. They are more in hiding and maybe hunted down since they are outside the guild's power and ability to control. There could be 'circles' or 'pact houses' that form around each patron and you have a fey group that tries to protect their own and a fiend house that may protect their own to a point, but all of them are against the guild.
Of course, if you are the guild and there is another way to gain magical might, you may try to control the patrons. The guild could have a fey lord that they sponsor and a demon lord that grants power but has his own plans. There could be a guild leader that secretly is a warlock and is trying to create a blend or bend the other powers to his control. Kind of like in most movies where the 'good' leader is secretly behind the plot to destroy the main storyline.
The way I was thinking about it, it would be... both. So if you want to be a warlock that isn't "in hiding", you take the one (or two?) patron that is approved/controled by the guild. But if you want another patron, then you are one of these renegade warloks.
I'll note btw that being a Guild Warlock doesn't mean that you have to be one of these "failed wizard nobles". You could be a student of modest means, brought on the Academy for their potential, and then who stumbled upon the "secret room" and became a warlock anyway.