I’m probably going to get a lot of flak for this but this is by no means a “troll” post. I’ve played the game since launch, experienced all content (WvW, PvE, and sPvP. ) This tier list is a compilation of several factors, including perceived strength as discussed in numerous forum threads which I have read or skimmed. Even though I have played sPvP I do not have enough experience in the matter to rate certain classes, therefore, and I am going to bold this, these ratings do not take into account strength perceived or otherwise in sPvP!
S Tier
Guardian – A Tier strength in WvW, A Tier strength in PvE.
Elementalist – A Tier strength in WvW, A Tier strength in PvE.
A Tier
Thief – A Tier strength in WvW, B Tier strength in PvE.
Warrior – B Tier strength in WvW, A Tier strength in PvE.
Mesmer – A Tier strength in WvW, B Tier strength in PvE.
B Tier
Necromancer – B Tier strength in WvW, C Tier strength in PvE.
Ranger – B Tier strength in WvW, C Tier strength in PvE.
C Tier
Engineer – C Tier strength in WvW, C Tier strength in PvE.
Reasoning Behind the Rankings:
Although one class might shine above all others in WvW and appears to be more useful than most, there strength rating, perceived or otherwise, in PvE might notch them down a ranking. This is why you see the Guardian and Elementalist so high up in the Tier list. What they bring to WvW and PvE is too much to ignore. I truly believe that in fractals and dungeons no one groans a little when another Guardian or Elemenatlist joins. The wealth of powerful options they bring to WvW outclasses all other professions. We all know the amount of support and useful utilities a Guardian and Elementalist bring to WvW (swirling winds, meteor shower, hallowed ground, stand your ground, etc.).
The three A tier classes were placed in these brackets because while they might shine or even overpower a S tier class in WvW they fall slightly behind in PvE, or vice versa. The thief is the most talked about and polarizing class in WvW, numerous videos are posted daily of a lone thief completing insurmountable tasks (soloing towers, soloing roaming groups, guaranteed Yak assassination, etc.). There perceived strength on the forums is nothing short of godlike, however they do lack slightly in the PvE department. I have grouped with many good thieves in PvE, however when compared to the A Tier PvE classes (warrior, elementalist, guardian) they are moderately outclassed. The mesmer falls into the same bracket, as they are also amazingly useful in WvW (Portal, Timewarp, Veil, etc) yet while they are supremely useful in PvE (Timewarp) they are also outclassed by the warrior, elementalist and guardian in that regard. Finally we have the Warrior. While certainly a true behemoth in PvE (they can solo dungeons…) and they are amazing in WvW (watch a top guild like Red Guard utilizing a warrior in WvW) they bring less group support to the table than the other A Tier WvW professions and do not have as much nifty tricks as the thief.