It really depends on where I'm having my pizza. As others have suggested, "mystery sausage" (i.e., sausage on a pizza outside of Chicago) can be problematic. Therefore, if I'm outside of Chicago, I'm not going to order sausage unless I know it to be good. So, it's gonna be pepperoni and green peppers (and mushroom and onions, if my eating companion(s) agree).

If I like the sausage, it'll be sausage and green peppers.

However, if I'm having thin crust pizza in NY, I'll just have cheese.

Two places where I only do veggie pizza because it is sooo good, are Harrod's pizzeria in London and Sopprafina in Chicago (a superthin crisp crust with spinach, red onion and mushroom).

I don't go for the weird California Pizza Kitchen ingredients like roasted potatoes, carmelized onions, etc.