A Banker is someone who gets mostly Defense weapons and strength. This is so that they can save their gold, or bank. Banking is good if you want to save up a lot of gold for upgrades or to buy morale.
A Slayer is someone who has most of their strength in their Strike Action. This is so they can attack people more and get more gold. Also, if you have a lot of Strike Action, you can farm (attack more than once every 24 hours) other players.
A Sabber has most of their strength in their Spy. This is so they can spy on people to gather information about their armory or sabotage people's armories to weaken the player. This is good if you are in an alliance and someone wants to know the stats of an enemy. This is also good if someone low hits you, you can sab them if they refuse to pay you for your losses.
A Ranker is someone who has good overall stats. They don't have one stat that stands out, but all of their stats are strong. This is so they can become the best rank they can. The good thing about this is so that no stat is too weak, but no stat is really strong either.
A Rouge is someone who is strong in both Strike Action and Spy. This is so they can farm players, mass players, and sab players. This is good if you really want to do a lot of damage to your enemy's armories.
A Protector is someone who doesn't like to lose their armory or their gold. They have strong Defense and Sentry. This strategy is similar to Banker.
Personally, I would not recommend Banker or Protector. Right now, in age 12, I started as Ranker, and went to Slayer. Choose the strategy that best suits you.