Leah,
To me your story about the apartment is, at its base, an issue about fairness in your relations with other people. The relative good of having an apartment -- yes, that's important to think about, but it really isn't what's at stake here. If you had singlehandedly found an apartment for your friends, which had one bedroom exactly like the one you're in now and three smaller ones, and you'd invited the others to move in with you, and they'd all said "Hey, Leah, just in recognition of all your work and how great we think you are, we all think you should get the biggest room" -- well, in that case, even if your living situation were *exactly* the same as it is now, you'd feel radically different about it. So the issue here is really, in my opinion, that you feel a bit badly treated by your friends.
My advice in this situation would be to deal with it before things get too entrenched. For instance, invite another friend for dinner and have them take a tour of the apartment and say conspicuously, "Wow, how do you guys deal with such an unequal room division? Do you split the rent differently?" Surely you have some friends who are vaguely naive and regularly say things like this anyway. You may even have suffered through many dinner parties where they put your friends through the wringer unintentionally. Now put this person to work for you.