San Diego runs from the bayfront and Balboa Park to beach neighborhoods miles up the coast. Downtown works for a short city trip. Stay in La Jolla or Mission Beach if your days are about the water.
Downtown has the Gaslamp Quarter, Petco Park, the convention center and the bayfront close together. The USS Midway Museum is on the Embarcadero, and Little Italy is just north of the office blocks. The Trolley runs through downtown, but a room by the convention center can be lively after dark.
Balboa Park's museums and the San Diego Zoo are just past downtown. North Park has restaurants and shops around 30th Street and University Avenue, and Hillcrest is west of the park. Both are handy for the park but too far to walk to the waterfront every day.
Mission Beach has a boardwalk and Belmont Park beside Mission Bay. Pacific Beach, to the north, is busy with bars and restaurants. La Jolla, farther north again, has the Cove and walks along the coast. It's a long trip back to downtown, so book a beach hotel only if the beach is the point of the stay.
Old Town, north of downtown, has the historic park and a transit center on the Trolley. The airport has a direct bus, Route 992, to Santa Fe Depot. In late spring and early summer, cloud can sit over the coast while inland neighborhoods are sunny.