That highly depends on what your main conflict is.

If you want a Man vs. World, in which you want the character more afraid of what is outside? Then you don't want a scary MC.
If you want a Man vs. Self, in which the character is more afraid of himself? Then you want a scary MC.

Personally, I tend to gravitate towards the latter. There's a lot of good juice in writing, in particular, a female lead who is terrified of her own dark desires...