Which of these best for condition build?

EngineerNecromancerGuardianWarriorWhich of these should I go with in case I want a conditions character?

https://snowcrows.com/ ?

Depends on your playstyle:

Zerging/Smallscale/Roaming Condi AOE Bomber -> NecroChallenging Condi Roamer/Smallscale -> EngineerCondi + Support -> FirebrandHigh mobility Condi Stealther -> Thief

Edit:You can of course also Play a roaming condi ele, that works also quite nice.And probably the most annoying: condi Mirage roamer^^

Please be Aware that, at least engineer in WvW, is no burst condi class, you have to Keep up constant pressure and make good use of your healing abilities. I recommend therefore to have a significant amount apothecary gear. But that is personal taste though :) I think many Play with trailblazer or similar Cond/Tough/Vita..

Engineers Condi damage is best suited for 1v1 or smaller scale combat.Necro got the AoE damage for larger groups and works best with support.Guardian can play cheese condiburst, better suited when roaming or in small grounps.Warriors condi is.. best in PvE (raids/fracts) .. some weird longbow berserkers in WvW zergs doing some work though.

Engineers for bombs, granades and some flames from pistols.Necro for giant circles that applies conditions.Guardian for "teleport into enemy and dump damage" gameplay.Warriors for.. longbow burningfields.. and bleeds with sword?

The biggest advantage for engineer is definitely in small scale.The sheer volume of different conditions they can apply in a short time catches many players off guard, especially when they don't have resistance or multiple condi cleanses.