Baja hands down...great weather, great people, great food, curteous drivers, great scenery, free camping....have a look at
my tour photos here. Fly to Cabo and ride back to San Diego a trip of ~1000miles.
It is a great ride! However, I would recommend flying to San Diego, and riding to Cabo. The prevailing winds blow to the south east, and it makes for a tough return. (I've done it. Won't do it again.)