Are left hand pitchers more difficult to hit for right hand or left hand hitters?

right handed pitchers throw breaking balls that break AWAY from right handed hitters and vice versa, thus it is generally considered more difficult for a right handed batter to hit righties. There are exceptions, the 'screwball' is an example. Generally a right hander wants to throw it only to a lefthander. Its not that common of a pitch. Recently the most notable example was Fernando Valenzuela and lesser known Jim Mecir.