If you are a new World of Warcraft player or seasoned professional coming back to Warlords of Draenor, there is always a certain class you might really enjoy. Depending on your personal preference, you might like tanking, healing, or DPSing (damage) more. Depending on your end game goals and play style, the class you pick will determine your ultimate game experience.
The Defensive Type Who Likes to Smash Things
If you happen to have a flare for protecting your teammates, keeping massive survivability, and slamming your shield into things, a tank might be for you. Warriors, druids, death knights, and monks all have significantly different tanking styles. Paladins are often considered the "easiest" tanking class but monks could come in a close second as long as you keep up Guard and use your brews. As hybrid classes, paladins, monks, and druids give you some flexibility as to what role you play. But if you solely want to tank while using a weapon and shield, warrior might be for you. Blood death knights can also provide the tanking role, depending on self heals to stay alive.
The Supporter Who Likes Watching Health Bars
Let's say you're not as crazy about hitting things and would prefer to buff and heal your teammates. if this is the case, a healer might be for you -- priest, druid, and monk being some of the strongest healers in WoD. However, shamans are also very powerful healers and can use Earth Shield to keep teammates alive.
The "I Like to Kill Things" Type
Let's say you don't care about team support or defense and just want to watch your enemy's health bars go down while putting out as much DPS as you can. The great part of WoW is that EVERY class now has a powerful DPS capability. Pure DPS classes include hunter, rogue, mage, and warlock -- so don't play these classes if you don't want to be locked into a DPS role. Consider also that pure DPS classes will put some extra competition on you to be the best of your class that you can and really get your DPS rotation down. Using talent calculators and DPS meters, as well as staying on top of class changes with each patch, can help you be a top DPSer who is in demand by many guilds and groups.
Use LFR to Pick Your Favorite Class
My advice is to roll each class that interests you, get to level 15, and try your class out in the group finder (Looking for Group or Looking for Raid) to see how well you'll like playing in groups. This will give you some sense of how end game will be for you in a particular class. For example, I absolutely can't play hunters in groups because I get bored and don't feel like I'm doing well as DPS -- but some people love playing hunters. So take some time to experiment and decide which WoW class is right for you.