If using fresh tomatoes, bring a large pot of water to a boil. With a sharp knife, make an X in the bottom of each tomato. Carefully drop into water and boil 1 minute. Remove with a slotted spoon and when cool enough to handle, peel off skin and remove core. Quarter each tomato, transfer to a large bowl, and using an immersion blender, blend tomatoes into a chunky purée. If using canned, empty tomatoes into a large bowl and briefly pulse.
Add oil, garlic, and crushed red pepper together in a 3-quart heavy pot. Cook over medium-low heat, stirring frequently, until garlic is pale golden, about 2 minutes. Add tomato purée, basil, sugar, and salt and simmer, uncovered, stirring occasionally, until thickened and reduced to about 2 1/2 cups (40 minutes for canned and 50 minutes to 1 hour for fresh).
While sauce is simmering, cook pasta according to directions until al dente. Drain and toss with sauce.
Transfer pasta to 6 bowls. Garnish with basil and cheese, if desired.