My first play in PvP was with Guardian. I got easily rank 10 in no time no sweat.
Like Pants said 19 hours+ unlimited stack of aegis for Guardians. They have defense and offense. I tried Warrior later. Guess what. Got owned really fast. Warrior is for me like offense and stamina/health/adrenaline. As for Thief, Mesmer and such I believe a more tricky stealthy strat is in its place. What I am trying to say. All professions have its weaknesses and strengths. You should know what weaknesses and what strengths that exist.
DIfferent professions require different gameplay.
One more thing. It is always useful level up at least 40 lvls in PvE before rigging you character in PvP. Practising skills is useful. Always a good thing to know what you’re doing^^
Good Luck