First of all, welcome to the game. As you have already read, each of the four classes you have mentioned have their advantages and disadvantages. I will not restate what is already said, but I would strongly encourage you to be patient when playing. Shattered Kingdoms can have a very stiff learning curve that takes a long time to adjust to. I would also urge you to spend some time learning basic game mechanics before jumping head first into PK. Sometimes, mixing yourself up with the wrong crowd can put you between a rock and a hard place - leaving you with the feeling you can never learn or explore because you have people who are constantly killing you.
While I would say you should always play what you seem most interested in, I would encourage considering one other class. Priests are very essential to this game.
Heal and
resurrection are two spells that are usually in high demand. As such, priests are often invited along to the more difficult areas of the game.