Leveling in WildStar is a complete joy when you realize you have two methods to accomplish this task. The first is the standard questing and the second is the completely viable and fast PvP method. You can reach level fifty no problem through PvP, but it does require a little bit of work and planning.
Understanding the Basics of PvP
When you enter a PvP match, you receive XP for being around a player death, for capping a flag yourself or being in the vicinity, and for winning or losing. The most substantial sum comes from player deaths (somewhere between 1% to 10% a game) and winning/losing the match. XP is a fixed amount, so you'll see larger gains at the start of a battleground's bracket than later on as you're a higher level.
The experience comes to about 20% to 30% at lower levels, to 5% to 15% a level. These aren't exacts, but let me just say that gets going rather fast if you keep winning a ton.
Best Battleground for Leveling
This one is hard - everyone says Halls of the Bloodsworn and I'm inclined to agree, but if you defend first and you're good at the game, you could easily get stuck for 15 minutes defending. Then have another 5 minutes attacking, where as in Walatiki you could end the game within the first five minutes and I rarely see a game get past 12 minutes long.
So, it's all personal preference, honestly. If you have a pre-made, you can purposely lose the defense at about 10 minutes in order to get through it faster. In the pre-mades I'm in, we can usually power through the attack phase in about five minutes. Assuming, of course, the other side is disorganized.
The Art of Pre-Mades
Pre-mades are ultimately a group of random players forming a pick-up group with a proper ratio of healers and DPS, along with the optional voice comms. They're superior to solo queues only in the sense they get the proper ratio of healers / DPS and maybe they have voice comms. So it's important to understand you can lose in a pre-made. There is no "instant win because you grouped in Illium instead of through the group finder."
With that in mind, when leveling through PvP, you're going to want to try and join pre-mades as often as possible. It makes it more enjoyable, less monotonous, and easier to actually play the maps as a team vs. randomly running around hoping that you're contributing in some manner.
I suggest forming your own if there isn't any out there. A lot of times just spamming up /pvp asking for others to join you will get you a flood of people wanting to join you in your plight to win.
Mixing and Matching
Questing is slower than PvP for me, but I also work really hard on making my gear as good as it can be and working with talented players to create a team that is constantly going in and winning. Your experience could vary and it might not be going fast enough for you. That's when you can mix and match questing in.
Quests don't need to follow every breadcrumb outside of the first map that you land at (before you can even PvP). So you can hop in at any time and go to most any outpost and start questing. I've gotten past level 40 easily without questing beyond a very small amount, but there can definitely be times where just zoning out and questing can be easier.
What about loot…
Hilariously enough, PvP gives you money, AMPs, decor, and gear that you can wear or sell. It's really lucrative. So you don't have to worry about that. Prestige also rains down on you, which is used to buy PvP gear, which is really fantastic for PvP. There are sets starting from the first battleground tier to the last. You cap at 5k, so be sure to buy up pieces as fast as you can equip them.
That's about it for leveling in PvP in WildStar. Hope you have fun in game!