The penis is made up of 3 main sections, much like long balloons - 2 at the bottom & 1 at the top, with the urethra nestled between the 2 bottom ones. When erect these 3 balloons fill with blood. It is not uncommon for one to be slightly shorter, or longer, than the other 2, thus causing a curve as a result. In my own experience the most common curves are upwards and / or to the left. Downward curves and / or to the right seem to be far more rare, but makes absolutely no difference to performance or quality no matter which way the curves lie. Personally mine is straight & at 90 degrees, so not even with an upward angle. Remember - appearances don't make the slightest bit of difference, so long as it does what it's designed to do - at which time most of it is out of sight for most of the time anyway.