It's normally the upper hinge that rusts cuz the warmest (and most humid air) rises.
Because the hinge pin might be rusty, it may also be hard to take out. I find that grabbing onto the head of the hinge pin with a pair of locking pliers and turning it back and forth WHILE pulling on the pin works best for removing it.
The best way I know of to clean the hinge pin up (once you get it out) is to put it in the chuck of an electric drill and hold a piece of emery cloth against it while it's spinning.
A hinge pin has a very easy job, and almost any lubricant will work fine on a hinge. I use Duralube (As Seen On TV!) only because I have some and don't use it for anything else. But, any grease (like wheel bearing grease or lithium grease or Vaseline (as already mentioned) will work fine). I wouldn't use WD-40though because it's such a light oil that most of what you put on will evaporate, leaving only a thin oil film behind that might not last very long. I'd go with any lubricating oil or grease instead.