Some of the best -- and juiciest -- burgers in town are at this simple North Beach diner. Mo's offers a straightforward but winning combination: big, thick, grilled patties of fresh-ground, best-quality, center-cut chuck; fresh french fries; and choice of cabbage slaw, sautéed garlic mushrooms, or beans and rice. Voilà! You've got the city's burger of choice (Zuni Café's is a contender, but at almost twice the price). The other food -- spicy chicken sandwich; steak with veggies, garlic bread, and potatoes; and token veggie dishes -- is also up to snuff, but it's that messy, memorable burger that keeps the carnivores captivated (the sinisterly sweet shakes are fantastic, too). Bargain-diners will appreciate prices, with burgers ranging from $4.95 for a classic to $8.75 for an "Alpine" burger with cheese, sautéed mushrooms, and fries. Entrees start at $9 for a roasted half-chicken with three sides and top out at $14 for New York steak. The classic breakfast menu is also a bargain. A second location at SoMa's Yerba Buena Gardens, 772 Folsom St., between Third and Fourth streets (tel. 415/957-3779), is open Tuesday through Saturday from 9am to 8pm, Sunday and Monday from 9am to 5pm. It features breakfast and burgers.