If you're on the cusp between the recommended height range of two sizes, the absolute best thing is to try to ride them both. At a minimum, check the stack/reach measurements on your current bike and compare it to the new model you are looking at to get an idea of a fit you are already comfortable with. If riding the bike is not an option, consider the following.

Body Dimension

Not all bodies at a given height are the same. If you have longer legs and a shorter torso than the average person your height, that may push you towards the smaller of the recommended sizes. If you're all torso and arms, most likely you'll want to size up.