I'd say San Jacinto was more than first intuition. It is the fastest-slipping southern California fault over the last few hundred thousand years. I'm not sure whether or not it now has the fastest GPS-determined strain accumulation because there is an extra 7 mm/yr now in the Eastern California shear zone (12 mm/yr instead of geologically-determined long term 5 mm/yr. Also, the San Jacinto is so close to San Andreas that it is difficult to distinguish the "flexing" related to one locked fault from the other one.

Also, San Jacinto system including southern splays has been probably the most active over time.

Chris