From what I know about playing defense, Hamrlik is better at restraining forwards from going to the net and at retrieving pucks than Markov. Just by a air though.
Actually they are pretty much as good as each other in their own zone, it's just that Hamrlik is a very patient player that plays with a ******** of poise and rarely makes mistakes. When you talk about Markov in the defensive zone, you enter the "unorthodox" territory. He has a very peculiar style when following forwards into the zone. His whole defensive play is more based on speed and stickwork than most "classic" defensman like Roman.
Georges well, he would kill his new born son to make a play along the wall... need I say more?