lets see them one by one and the benefits they get from killing benazir:
PML N - due to her death they were not able to win the elections and now sitting in opposition.
Musharaf - this event has defaming effect for musharaf due to the involvemnet in BB s killing accusations.
Taliban - no benefit except more people become against them after this event. they definitely get some fame from this killing as an extremist organistaion and their capablities, so people satrted taking them more seriously
Zaradari - only benefits, no loss other than of his wife. premiership now came in zardari family which was in bhutto family before. now zardari family owns the PPP which was bhuttos product. he became president and won the election with huge majority which he never would be able to do (alone).
i think the only person who get benefitted the most from the death of Benazir bhutto is her husband and we all know the capabilities of zardari (Mr.10%) so i think that was zardari who killed her. may be there are some other elements involved in it as well but main was zardari.
regards