Weakest lvl 5 class/subclass for a npc encounter

I want to design an encounter for a party of 5 people in a westmarch. The party will be lvl 5 and 6, and will have some magic items, potions and scrolls.
To make things short, the players want a tough combat and dont care if the pcs die, so I want to give them that. A balanced encounter, as they will be face another party that will have player levels. This party will play smart, try to target the weakest characters first, focus fire and hit them in the ground when they get to 0 HP.
While this may be dangerous, the real party should have more resources in form of items, potions and other stuff, but I was wondering wich class/subclass should I make the enemy so they arent that deadly. Maybe 5 rogues? or rangers?