The tool pictured above is a European style cutter from Williams-Sonoma. Have you tried it? I usually use my large chef's knife to cut pizza. It's long and heavy and can cut through most toppings with a single, firm chop. I enjoy having yet another use for my multitasking chef's knife and since my kitchen drawer space is limited, it's nice not having a another tool to house (although I know a pizza cutter has many other uses besides pizza!).
Here's how I do it: I position the knife with the handle towards the crust and the pointy end towards the middle. Using one hand on the handle and the other on top of the blade, I push down with a fair amount of force which usually results in a smooth, thorough cut. Depending on the size of the pizza, I then go to the opposite side and complete the cut using the same method, so the pizza is now cut in two. I then work with each half, cutting it into three or four pieces. The whole procedure takes me 20 seconds at the most.
What I don't like to do is drag a pizza cutter through my pizza, although I admit it's been a while since I've owned one. Maybe they've improved over the years? Tell us what tool you use and why in the comments!
Related: Really Manly Pizza Cutter