My personal experience is that the SOMA-Moscone area will have fewer transit options. All other areas you mentioned will have access to BART, cable car, and light rail. You should be safe walking alone any of your choice areas, except maybe really late at night. The Embarcadero area is quieter in the evenings than USE and USW. I've seen the Parc 55, a 4* in USW (great location by the way), and the Hyatt Regency, 4* in the Embarcadero win for $85 regulary. I've stayed at and enjoyed both. --Vince
