Now that Theo's Pizza is closed it's a tough call what Dorchester's best pizzeria may be. Heaven knows there are plenty of them. It's hard to say many of them have any defining characteristics beyond address though.
If you've travelled New England any length of distance and stopped for a pizza, you know the standard New England pie. The crust is neither thick nor thin but somewhere in the middle, just enough to absorb all the oil that leaks out of the shredded, wholesale, industrial mozzarella. The sauce is ladled out of a gallon can. The seasoning is oregano. I haven't been to every pizzeria in Dorchester, I haven't the time, but from what I've sampled Dorchester pizza chefs don't stray to far from the New England paradigm. They shouldn't really. I'm a Nutmeg Yankee and I'll order a Dot slice over a New York or Chicago style pie any day.
As with many things, if you are moving to Dorchester, don't get your hopes up too high for high-faluting pizza. As with everything, you will find that what is in Dot will hit the spot. If you take the Red Line to Field's Corner, I'll meet you at Hi-Fi.