School is probably the worst. On a college campus there are lots of students, in other words, lots of potential zombies. Plus in any classroom there's pretty much one entrance/exit and nothing that would make a suitable weapon. If I could get out of the classroom and then out of the building, then what? I'd most likely be in the middle of campus. I don't drive to school, so I would be pretty much stuck there, unless I could find someone with a car who wasn't zombified.
My house is not very fortified. The doors would probably hold for a little while, but we have a huge window that would be a perfect entry point for a shit-ton of undead. I could probably barricade myself in the basement, but zombies could still get through the back door pretty easily. And if I'm stuck downstairs I'm pretty limited on my weapon choices and food (assuming they can't get through the back door and I have to wait them out) - we have a pantry downstairs, but there's not really a lot of food in it.
Work is probably the best of the three. No matter what library I'm at, I'm still at a library. That means there are lots of people around. There are usually several ways to get out (and in, unfortunately) so I could possibly escape out the staff door and maybe make it to my car. I would have a hard time finding weapons, but there are plenty of book-carts and other obstacles that could slow the pursuit.
Yes, I have gotten in the habit of scoping out any setting I find myself in and thinking to myself "What would I do if zombie burst in right now and started chewing on people." It's silly, I know. But it never hurts to be prepared. Not that it will really do me much good - if I survive zombies it will be due to sheer luck.