I struggle to think of any class that a Rage Juggernaut is good against 1v1. The spec is quite simply not designed for a 1v1 fight because it has little "control" and they have one defensive cooldown and no more. In a duel situation, it's easy to pay attention to their stacks of shockwaves as well which makes it easier to counter them. They really only shine in a team.
Vigilance/Vengeance has one brilliant perk to counter the sneakies, you just need good reflexes. The moment you're knocked on your arse, you have to pop Enraged Defense/Focused Defense (presuming you took the two skill points in Defiance/Unyielding). That's 15% damage reduction to their opening burst right there; after that, Push, Leap, Master Strike/Ravage - if the Assassin pops Force Shroud instead of Deflection, it's game over basically
But yeah, Deception/Infiltration is fearsome right now. I duelled a guildie on my Assault Vanguard and I just couldn't beat him. Force Shrouding Ion Pulse, Deflecting High Impact Bolt... I'm pretty much out of ideas at that point