Straight-six engines were historically more common than V6's, mainly because the length of such engines was not such a concern in rear-drive vehicles but also because V6's (unlike the 90-degree V8) were somewhat difficult to make smooth-running. The widespread use of front-wheel-drive and "east-west" engine configurations saw that the shorter engine length of the V6 became highly desirable, and these days most six-cylinder engines are made in the V configuration (in fact, the Australian [Ford Falcon]? remains one of the very few straight sixes still in use in contemporary passenger vehicles (oh, and some Mercedes and BMWs)).
see also V12