
click to enlarge
On your way to 18, you're going to want to max out your Gatling gun, windmill, silver bullets, windmill, and grenade skills, for easy leveling. The rest of the skills are optional and fun (especially BBQ and Flamethrower!) but I would recommend just getting the above skills for the quickest and easiest road to your class change.
Gatling Gun will do a devastating amount of fixed damage in a line, knock back and shoot through multiple opponents, and has a relatively low cooldown, but high mana cost.
Windmill is your close range get out of trouble area of effect knockdown attack, great in both PvE and PvP it will do a heavy amount of damage and trip up your opponents.
Silver Bullets adds a healthy amount of extra damage to your basic attacks, making it great no matter what weapon you happen to be using.
Grenades are some of the best AOE offered in the game and they LAUNCH your foes into the air, enabling great combo setups with your other skills. Try a grenade, then windmill them when they get up - most groups of enemies (and players!) can't survive it easily