It depends on what else you're doing for the week, but I would probably stay closer to Sea World. Legoland is in the north half of the county while most of the traditional tourist destinations (Sea World, Zoo, Balboa Park and museums, Old Town, Gaslamp Quarter, the Bay, etc) are all in the south. If you are traveling between the two during rush hour (around 3 - 7) it could take much longer. Mission Valley has many hotels to choose from, although be sure to look at recent pictures. A lot of them have been rebuilt recently since they were built in the 60's-70's but some are still original. We like the Doubletree Mission Valley of the ones in that area. Downtown and Gaslamp District also have a lot of hotels, but the prices will be higher in that area. Great nightlife down there though if that interests you. If you are looking for more of a beach resort/pool scene, the ones along the harbor are great, but those are the most expensive.