The best pizza I've had in New Hampshire is Crush Pizzeria's in Nashua, though I need to add the qualification that I've only been twice, and have tried three of their pizzas - there may well be duds on the menu. (I've also been at fairly non-busy times in the afternoon.)
Crush makes Neapolitan style pizza: thin crust, cooked quickly (a couple minutes) in a very hot wood-burning oven (900 degrees), so that the crust blisters and blackens in spots. It's a style that lends itself well to fresh mozzarella, and Crush uses fresh mozz from both cow's milk and buffalo milk (for $3 extra). I've had both and have no specific recommendation - both are very good.
The sauce on the red pizzas is just crushed tomatoes. The crust really plays a bigger role in the flavor here. It's a side effect of the style that the center of the pizza - the tip of a slice - can get a little soggy, but don't worry about it.
Like I said, I've had three of their pizzas. Two were red: the Regina, with buffalo mozzarella, grape tomatoes, basil, and olive oil;
the Salsiccia, with homemade sausage (crumbled and mild), red onion (they like red onion at Crush), basil, and olive oil;
and the last (ordered on both occasions) was a white pizza, the Pista: fresh mozz, parmigiano, red onion, fresh rosemary, pistachio, and olive oil.
The Pista was by far the best, and is inspired by the Rosa at Pizzeria Bianco, widely considered the best pizzeria in the country. I haven't had the Rosa, but the Pista is amazing - much moreso than you would guess from the ingredients, and yet still recognizably pizza (it helps that so much flavor comes from the crust and the cheese).
Multiple pizzas use either black truffle paste or truffle oil, and while I generally don't like the use of truffle oil, in this case it seems to be used to intensify the flavor of pan-roasted mushrooms, which is probably its best use. Crush isn't cheap - pizzas are personal-size and hover around $12-15 - but with pizza so simply seasoned, you really want the best ingredients.
I'd like to see a red clam pizza from them in the future, and something spicy like a broccoli raab/roasted chile combination, and something with burrata. But if I'm thinking about pizzas I wish they made, you know I like the place.