Before you choose your armour it's worth thinking about two things that you need to consider, armour class and coverage.
Most of the games in UK larp split leather armour into two classes, light armour and medium armour. Light armour is usually made from leather which is about 2mm thick, medium armour is made from leather 3-4mm thick. In the product listings anything that refers to medium weight leather is going to be light armour and anything which mentions heavy leather is going to be medium armour(helpful I know) anything made from lighter weights of leather, around 1mm such as hoods or leather trousers doesn't count as armour, just clothing.
Some of the smaller club games also have nuances to the armour class with the addition of extra metal plates and studs increasing the armour value.
Coverage is the amount of your body/body location(arm, leg etc) which is covered by the armour. Most games have a 50% coverage rule which means that at least 50% of a location has to be covered to gain the protection of the armour. So if you've got heavy leather greaves(leg armour), vambraces(arm armour) and a cuirass(torso) you can claim medium armour at a lot of games. Adding more armour in these games doesn't give you any more protection but does look cool and can make you feel more heroic.
Other games have different rules, where armour only counts on the area it covers. If a blow hits an unarmoured part of you then it's hit flesh, get ready to fall over.
And of course there are games that fall between the two and caveats about special hit calls but those are things that will be specific to your game. If in doubt it's always worth chatting to the refs/game organisers before you click “add to hoard”.