Generally the 60% off is better but you should always price the BCC and current X offer out as the BCC often has differing fares.
For even number purposes, let's say you found a cruise you want at $1,000/person and your a party of TWO.
60% off both = $800 for TWO. $1000 x 2 x .4
75% off second person = $1,250 for TWO. $1000 x .25 + $1000