In PVE, Moongoose is better.
In PvP, Executioner is better on target that have 3k-ish armor (Mage, Priest, Warlock, Rogues), unless you EA them, then it is redundant with the natural Armor Pen built in with the pvp set. Mongoose is thus better against everybody else and is really sick if used in conjunction with EA.
So as a general rule, yes, Mongoose is better for both pve and pvp.