Here's what I think of all the classes...
Archers- I hear that they are a fun class and I agree with those people. All they need is better ways of using their skills and slightly more attack damage. They still appear here and there, but they won't last long when the player realizes they won't be able to grind or compete with other classes. As players start to notice that the other classes are much better, they will switch and just making the archer class instinct.
Cowboy- Way too over powered by the use of spam. Most popular class used only because of the ability to spam anything. Back in the day, mages and archers were more popular due to the ability to spam arrow rain and thunder. The popularity of a class just seems to be about how much one can spam and the damage done from it.
Mage- A ton of damage in one blow. Over time, they are still over powered by the cowboys spamming skills. By still having the ability to heal allows them to be one of the most supportive players in a GvG battle. With the right skills and tactics used, its about the only class able to survive and defend against a cowboy's shotgun.
Warriors- Another one of those weaker classes. A warrior can't defend their selves against any other class due to poor range. Simply can be over powered in both players v.s players and players v.s monsters. You would be required to buy a private server just to be able to grind.
Most of these things have been said, but its just another way to put it and agree...