What is the best class for level 22?

The class you use will depend mainly on how you like to play the game. This usually comes down to farming or raiding. The trader is good for helping others and the builder can be useful to make the large upgrades you will need to do a little easier.

But generally most players either choose the farmer or the raider. If you are already using one of these then only change if you want to try a different play style. The farmer is safer and and will let you produce more resources without fighting. Good if you have less time or prefer less conflict. The raider will give some benefits if you like to take part in kill events, doomsday etc. You will need to do more active attacking though to get more resources and be more careful that you don't get attacked yourself.