I personally would like to see Adam Schiff, because this is someone that pisses Republicans off the most, however that risks losing a seat in the House.
Here’s some other options:
Representative Karen Bass
California AG Xavier Becerra
Long Beach Mayor Robert Garcia
Representative Barbara Lee
Secretary of State Alex Padilla
There’s also a slew of other candidates.
Edit: Under California Law the Governor nominates someone which after 2 years they must run for re-election.