Mushrooms (standard) or Sundried tomatoes - Love them both, but I mushrooms are more versatile and I think harder to get sick of.
Sausage, green pepper, and onion or Meatballs - So...if it's crappy sausage, not the first one. If it's decent sausage, maybe the first one. The combination is just excellent. So...mmm...well, let's assume it's decent sausage.
Steak and onions or Ricotta cheese + fresh garlic - Sausage is generally of better quality than most steak I've had at pizza places. The latter is just such a clean, delicious, wonderful topping combination that it's hard to beat.
Beef, onions, and green peppers or Pineapple - All about the beef - if it's shitty, it ruins it. A bit closer than the steak/onions, and I could have gone either way. But pineapple is so damn good, even by itself.