For me with upright bars it's easier to go smaller than it is to go larger. You can always raise a seatpost. But, it's impossible to lower a frame. Unless you got mad welding skills. Smaller bikes are usually lighter & quicker too. Now with drop bars, that's a whole different discussion. Perfect fit becomes very important with drop bars. Of course, I avoid riding drop bar bikes unless it's absolutely necessary. They're so damn uncomfortable.