If elected to the Senate, Kamala Harris would be on the road to the White House; if elected to the Senate, Loretta Sanchez would never be able to go any further. Just for that, I’d vote for Sanchez (and then take a long shower).
I wouldn't be so sure about that. As another poster noted, Sanchez is ambitious and has a national network of supporters. The RATs would LOVE to put a Latina on a presidential ticket and pat themselves on the back for "making history", and she's be one of the only prominent ones available.
The demographic trends of California favor Sanchez, but the hard-left Dem base is more likely to back Harris.