what is more stable benzylic or allyic ?

An allylic cation is a carbocation with the positive charge on an allylic carbon; an allylic carbon is a carbon adjacent to an sp2 carbon of an alkene.
CH2=CHC⁺HR ALLYLIC CARBON
A benzylic cation is a carbocation with the positive charge on a benzylic carbon; a benzylic carbon is a carbon adjacent to an sp2 carbon of a benzene ring
C6H5C⁺HR BENZYLIC CARBON
An benzylic cation will have more resonating structures than allylic cation ,more resonating structures contributes more stability to benzylic cation.