B737 CREW LANDED WITH 25 DEG FLAPS INSTEAD OF THE INTENDED 30 DEG FLAPS.

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BIG SUR TWO ARR INTO SFO -- ANTICIPATED AND RECEIVED TIP TOE VISUAL TO RWY 28L. THOROUGHLY BRIEFED (30 DEG FLAP) VISUAL AND ILS TO RWY 28L. IN DSCNT FROM 5000 FT ALT RESTR AT MENLO WERE GIVEN APCH CTLR (FREQ) CHANGE. NEW CTLR CHANGED CLRNC TO QUIET BRIDGE VISUAL RWY 28R; GAVE US PARALLEL TFC AT 9 O'CLOCK POS; AND PRESSED US TO CALL THE TFC; BRIDGE; AND RWY IN SIGHT. SCRAMBLING TO COMPLY; I LOST SITUATIONAL AWARENESS AS I SET UP FO FOR APCH. BACK IN LOOP REALIZED DSCNT WAS NOT FAST ENOUGH AND (TEMPORARILY) PUT FO TO 40 DEG FLAPS TO GET DOWN. ON GS MEANT TO RETURN TO 30 DEG FLAP; BUT SELECTED 25 DEGS. REALIZED ERROR WHEN VOICE ALERT ACTIVATED. SPD WAS ADEQUATE FOR 25 DEG FLAP LNDG AND HAD FO CONTINUE NOW STABILIZED APCH TO A PROPER TOUCHDOWN. PROBS: FO NEW TO AIRPLANE REQUIRING MAX SUPERVISION. DEMANDING VISUAL APCH COMPLICATED BY LAST MIN CHANGE BY CTLR. MY JUDGEMENT ACCEPTING NEW APCH THAT OVERTASKED ME. (I WAS VERBALLY FLYING THE APCH AS I SET UP THE FO AS I MONITORED PARALLEL TFC AS I HANDLE THE RADIOS. EVEN WITH VETERAN FO WE WOULD HAVE BEEN CHALLENGED; BUT COULD HAVE ADEQUATELY HANDLED THE APCH.) MY JUDGEMENT ACCEPTING; ALBEIT A SAFE LNDG; ONE THAT WAS NOT WITHIN SOP. A GAR WOULD HAVE CREATED ITS OWN PROBS; BUT WAS THE PROPER RESPONSE.