cgminer is the real hash rate. the pool calculate an approximation using nb of share and pool diff. most pool are a bit off most of the time up from what you really have but this always depend on luck so. cgminer is the real, the poll is the efficient hash rate a bite like the network hash rate is the time between block and diffculty, the network don't add miner hash it approximate what it should take to make the block at the actual rate.
+1
The pool tries it best to guess your hash rate by how many shares you submit in a period of time.
And let me tell you this.. miners would rather see it a bit higher then a bit lower. Being higher by a tad
generally results in less questions ;-)
