I have actually talked to several scouts about this issue. It really depnds on the mental makeup of the particular kid.
Playing college baseball teaches you discipline. Not only do you have practice most days and games on the weekends but you also have 15 hours of classes and that many hours over of studying. A lot of players are required to go to drills and study sessions as well. Mix in the fact that they leave on Thursday every other week and still have to keep up with their work, it is a huge test of character and discipline.
On the other hand, jumping straight to the Minors will allow you to focus a lot more time on baseball. You will be around better coaches, players, and managers. You learn how to be a big leaguer right off the bat. It also gives you a lot more free time and sometimes 18-21 year olds can find less productive ways of spending it.
If a player is a mature, driven individual they can absolutely succeed by going straight to the minors. If a player is still a highschooler more than physically, college can really benifit their career. Not to mention the many other great life experiences and education that you get by going to college.