Use armor if you are learning since its the early game go to and since you are probably a shitter that doesnt know how to tank camps youll probably be better off using them.
4 armor 5hp helps you early while also giving you some mid/late advantage, there are quite a few champs that can do this and if you are good at tanking camps you can do this in almost every champ with no drawbacks whatsoever.
9hp is for mid/late advantage but this should only be used in a couple of junglers that already have no difficult with camps early like graves or champs that want to have a really strong mid and/or late like olaf and hecarim. You should only do this if you know how to tank camps though otherwise you will just fuck urself.
Just use 9 armor for now and watch some streams or videos and try to learn how to tank the camps and what route you should do. You will eventually learn what runes fit which champs.