Toughness or vitality?
I stack vitality for my condition\condition defensive Engineer, I find that I can live for a long time and I rarely die 1v1. I last a long time in group combat as well.
I’ve never tried stacking toughness though.
I can’t say anything categoric from experience, but I know a lot of warriors (already in Heavy Armour) will not stack Toughness, due to its current perceived lack of value in only pertaining to a specific damage type, i.e. direct damage only.
[See http://wiki.guildwars2.com/wiki/Damage]
Therefore, it does not contribute any defence towards incoming condition damage (bleeds, poison, etc.) or falling damage.
Vitality of course, is converted into a measure of ALL damage taken (direct, conditional and falling) before entering a downed state; so in terms of the view expressed by such warriors above, can be considered more valuable than Toughness. But of course, this could just be because they are already starting from a higher point with the base defence bonus generated from wearing Heavy Armour.
My personal experience and testing shows that toughness mitigates a very noticeable difference more health then what vitality adds in comparison to damage taken. At least where direct damage is concerned.
As far as condition damage is concerned, vitality definitely wins out.
I like to go full vitality/tough for an indestructible E-Gunning, condition cleansing mass bombing weapon of destruction. :p, but if inhad to go one way or the other I’d say tough. Only bc I’ve roled high vitality and had my hps melted so quick which is the main reason I like a tanky build.