The harder the hit the more exp gained.
http://www.uesp.net/wiki/Skyrim:Heavy_Armor
Note that when leveling up heavy armor/light armor, you HAVE to take damage from an outside source (i.e Equilibrium(Alteration skill) does not level up your armor)and the amount of damage will dictate the amount of experience you gain(NOT the number of hits you take) One way of leveling up heavy armor is by fighting with giants. From a starting level of 15, by training against a giant, you can reach a level of over 50+, within 5 mins of getting bludgeoned, provided you dont die. A restoration spell(Healing, Grand Healing etc) would be most helpful while training. Note that at early levels try to avoid the Giant's ground shatter attack with his club, Unless you have a lot of health to spare.
Find a giant/mammoth/troll to power level. Just be sure to have plenty of potions.