The one visual novel I am familiar with, Snatcher, has its main character's dialogue as one of the highlights of the VN, the buddy-cop nature of his interactions with his robotic assistant.

So it all depends on your story. Is the main character meant to be a blank slate, someone for the player to insert themselves into the shoes of? Or are they an established character with a personality of their own? One type of story isn't variably better than the other.

Of course, there's middle-ground between the two. Mass Effect has a degree of set personality to the main character, but you can choose their dialogue choices and whether they take more diplomatic or aggressive choices. Dragon Age II also has a very novel system, where your dialogue choices determine the main character's personality, which flavours minor dialogue and gives additional options in some circumstances.