I was told that oral can be an intense experience for a man, since you can do a lot down there with your hands, tongue, mouth, and throat, including the vibration you can create with your vocal cords.
Meanwhile, penetration is also great. It gives both participants a different level of intimacy that oral could not equal.
It all depends on individual preference, and what you both agree upon. Variety is important, as well as proper timing and technique.