The game is fairly easy and you'll get in very quick. So, forget about "best", "optimise" or other ***** like this. Pick the class you like the most, level up, unlock all spe, try every weapon, take the time to READ all the skill & trait and understand the synergie of them. Once done, stat, role and so will become obvious to you.
GW2. Best Open World Build. Celestial Herald. Revenant PvE. The Celestial Herald provides incredible sustain, good damage, very good utility and CC, and permanent quickness as well as many other boons for allies. The build touches nearly to immortality with how much healing and damage reduction it stacks. Mainly use Mace/Axe.
It also has the least builds in pve content of these 3 options. And guardian lacks mobility. Although willbender has alot more mobility. Its a single specc of the entire proffession, the other 2 are generally alot slower. Compared to thief or mesmer. Guardian is prollly the strongest pve proffession.