Which kind of bowlers are hardest to score from?

i think the bowlers who do not bowl so fast are the hardest to score from as long as they are accurate. With exess speed the batsmen can use the speed to guide the for ones and twos but with good medium pace bowlers it is much more difficult. For example mitchell johnson and dale steyn who are fast bowlers have an economy rate of 5+ but shaun pollock who was a medium pace bowler has an economy rate od less that 4