I would go for the reward nights at the US Grant. It is an old and historic hotel that received a much-needed makeover a few years back. There are not many grand old places like this left, so it is a good experience. 12k points makes it a very good deal. It is literally across the street from the outdoor Westfield shopping center in the heart of downtown and the Gaslamp. It is not the best option if you just want to stay in the hotel, but it is a very good base for exploring the area.
Laguna may be the best 'resort' option, but it could be a long drive. There is also not much to do in that area, so you may get bored if you are interested in exploring. You would be going against the typical weekend migration from LA to SD, but there are still numerous bottlenecks on that route. Traffic anywhere on PCH on the weekend is always bad, especially around Laguna. If you do decide to go that route, try and take the coastal roads (Coast Hwy, Carlsbad Blvd, PCH) all the way. You would only need to take the 5 freeway between Oceanside and San Clemente. It does not take much longer, but is much more scenic.
If you do not like heat, stay away from the high desert. Better to visit between October and February.