I must respectfully disagree here.
10 seconds major expedition (and major endurance too) which does not break upon entering combat. Requires no enemy target and that is the unmorphed form. Compare to other classes:
Nightblade's cripple: 8 seconds major expedition, requires a target to cast. Does not break upon entering combat. Reflectable, dodgeable. Edited to add Double Take: Gives 4 seconds major expedition, self buff, does not break upon entering combat. Edited to add Path of darkness: major expedition while on the path (10 s skill duration) and up to 2 s after leaving the path.
Dragonknight's chains: 6 seconds major expedition, requires a target to cast. Does not break upon entering combat. Not reflectable or dodgeable.
Sorcerer's Boundless storm: 6 seconds major expedition, self buff, no target required. Does not break upon entering combat.
Templar's...hmmm...well...yeah...they can roll dodge with a bow, I suppose?
Rapid maneuvers: Alliance war skill, major expedition for 30 seconds. Breaks upon casting any skill upon an enemy or ally. (attacks, heals, almost anything).
It seems to me that Warden got the longest duration skill of all classes. The morph that also gives you minor berserk, in my opinion, would out-perform the other class-based skills, but is not too crazy OP in comparison with the other skills.
Edited to add other nightblade class skills. Thanks to @paulsimonps for the reminders