Pizzeria regina is in the copley mall (attached to your hotel), but for the real deal Regina pizza you could walk about 18 minutes or so to the north end and visit its original location. The oven there is an ancient oil burning oven that does make a different pizza than any of the other locations. This is probably my favorite boston pizzera, and I feel like the north end of boston (our little italy) where the original pizzeria regina is located is a must see if you are visiting this city. While you are there you can walk across the street to fanuiel hall, which is a fun spot to shop or hit up a bar for some drinks. The original North end location only sells slices for lunch, but all other locations (including the copley mall) are slice friendly all the time. A cab ride from your hotel to the North end location will be about $10 with a tip.
Pizzeria Picco is a very unique pizza, and its only about an 8 minute walk from your hotel. Its nice because its not made with bromated flour, but it can be expensive for the amount of pizza you get. No slices here.
New York pizza on Mass ave is about a 10 minute walk, and is a very authentic NY style slice. Its open late and always has a few types of pies available in slices. I crave this place if I haven't had it for a while. Its just as good as 90% of the pizzerias in New York. Its right on the edge of a bad neighborhood (which you won't have to walk through), so you might want to visit durning the day. I lived across the street from it for years, and it never bothered me, though. There is another New York pizza in the theater district that is basically the same pizza, but for some reason I still prefer the Mass av. location. If you like Jazz, its right next to a very tiny but fun bar called Walley's that usually has a good band playing.
Little steevies pizza is only about 4 minutes from your hotel/convention ctr., but can be VERY hit or miss unless you trick them into making you a fresh pie. Its actually on the same street as the convention center (boylston), and you would have time to hit it up during a quick break. To ensure a fresh pizza there you should call ahead an order a small or medium pizza. They make tons of large pizzas up ahead of time and have them sitting around for hours. The nice thing is that this place is open until 3 in the morning, and it does sell slices. Every now and then you get lucky and even a slice here is amazing, but its usually more miss than hit.
Bar10 is actually attached to your hotel and has some excellent thin and crispy cracker crust pizza. Its a hotel bar, so you will find lots of cougars there. No slices here, but they are small personal sized pizza.
Right next to the airport is Santarpios pizza, and I have often left myself an extra hour or so to stop here for a pizza before hitting the airport. You will be driving right past it to get to the airport. You could even call ahead and have your taxi driver stop out front so you can run in and get your pizza to go on the way to the airport.
The Upper crust is not my favorite pizza in Boston (they use a rolling pin uggg), but I have to mention it because its very close to you (newbury st), and many people love it. It often wins awards for best pizza in the city. They have an unusual sauce which is stanislaus tomato filets, so its basically all chunks that burst with a fresh flavor. They will deliver to you
Also not my favorite is the Greek style of pizza that is very popular around boston. Its basically pan pizza made with white cheddar cheese. The dough is left to rise a little in the pan with some oil in the bottom, so its light and fluffy with a bit of crisp and fried flavor to the bottom (if its done right). If you want to try it you can go to a place called despina's place for one of the city's best versions of that style. its about 5 minutes from you as well. Im not sure if they sell slices any more, so if not you could walk right over to Supreme house of pizza on mass ave. to try the greek style in slice form.