Q.1 Which is more stable?

Phenyl or venyl- carbocation

Q.2 How r-effect in hyperconjugation let to stability of free radical?

carbocation is SP2 hybridized and the charge is a result of the empty P orbital. A simple way to think about this is to consider that carbon generally doesn’t like to be positively or negatively charged, so in this case it is trying to get some negative charge (which would be the electrons) to balance the positive charge at least as much as it can. It turns out that these electron density can be provided by the neighboring SP3 orbitals of the C-H bond which partially overlaps with the empty P orbital.