In comparison to Light Armor, the Medium Armor sets are heavier, therefore leading to being slower, but, in turn, Is much lighter than the Heavy Armor sets, leading to being faster during combat, and this will play a large role in how you play the game, ranging from PvE and PvP.
It is recommended that New players start out with mostly Medium Armor Sets, and they can make a decision for themselves. If they find they are taking too much damage, then they can make the choice to switch to a Heavy Armor Set, and if they feel like they are too slow, or they take too little damage for the defensive properties to be worth the weight, they may choose to choose a Light Armor Set.
A good choice is to mix up armor sets. Maybe you want some heavy chest armour for the superior defensive properties, and then you may want to have a medium helm, just to be defensive but not increase your load in weight, and then maybe have some light hand and foot armour, to counteract the weight, and keeping your load to a minimum, while still getting a small defensive property.