I’ve come to notice that I normally don’t use characters (NPCs) that I don’t like. I’m not really talking about not using straight warriors because I prefer magical types, but that happens too. I’m talking mainly about personalities. If I don’t like the mission giver, I tend to drop writing that mission in favor of ones where I like the known associates. I know I’m missing something here.
GMs have to include characters they don’t like. Think about most stories (TV, movies or books). The good guys do not always like each other. They may have completely different goals, but still want to do the same missions. More to this point, they might be completely different personalities. Even different personalities than the GM. Yep - you need to play against your own personality. If not, then not only do you become boring (a one trick pony), but you become predictable. That’s the big fear! You as a GM cannot be predictable. Kiss of death! If they know what to expect, every one of your twists and sub-plots will be telegraphed.
Covering more ground here than planned, but it needs to be said: GMs need to play against their type. Use NPCs that are different from you, different from your personality, different from your style of play. If you don’t remember to keep this sort of variety in your campaign, you’re doomed. (OK, that was a little overdone, but I hope you get the point.)