Since they're supposed to be the bravest of the brave, why wouldn't the Gryffindor Common Room be in the tallest tower in Hogwarts. The portrait guarding it currently appears to have about as much grace as its residents too. Sorry if my disdain is evident but if it's such a problem just go courage yourself off a cliff will you?

In an attempt to make access as inconvenient as possible so only the really motivated students can get in, the Ravenclaw common room is located on the west side of the castle up a tall, tightly-winding staircase. As if this physical exertion wasn't enough of a test the door itself has no handles - rather students must answer a riddle to get into the common room. It begs the question - how many sleepy Ravenclaws does it take to get to bed? Depends how stupid the riddle is, I suppose?