How about the Survivors from both Left 4 Dead games?
They would be hard to kill (maybe with regenerating health or maybe they would have reusable medkits with a cooldown, kinda like rebel medics), have high damage output, and could maybe use the same lines as the Survivors in-game.

Name: MTF Elite
Description: SCP oriented NPC. Uses grenades, and can swap weapons by your command of Alt + R on a weapon. 300 health, if "killed", he's injured, meaning he falls on the ground and cannot move. He will use his Radio to communicate that he needs help. He deals 3x the damage with a gun, and has 1/3rd the bullet spread with TFA Base [Reduxed] and Standard weapons.
Model Link: MTF Guard PM and NPC

Possible secondary ideas to him:
1. At the command of Alt + R on a health kit / health vial, he picks it up. He can hold up to 3 health kits. The highest he's ever had in health kits is called "Medkits". Medkits + 3 = Amount of health vials he can hold.
2. He has a limit on how many grenades he can hold. He can hold 10 spare grenades, but he gains 1 grenade / minute until he reaches 3 grenades. Upon throwing a grenade, he loses 1 grenade.
3. He regenerates health when outside combat.
4. If he takes fatal damage from SCP-173 he dies permanently instead of being knocked down. Same goes with 049 and 096 from the collection that the maker of the SCP-173 mod made.
5. If he takes fatal damage from SCP-106 he is pulled into 106's pocket dimension. Upon this, 106 disappears, he takes 50 damage, and if he takes non-fatal damage from this, is pulled down into the ground with a scorch decal under his feet. If he takes fatal damage from it, he dies, and a couple scorch decals are scattered across his corpse. For the sake of gore mod compatibility, also make this corpse take 1 damage each second. Back to non-fatal. After he is pulled into the ground, 106 is respawned to get a new kill, out from that scorch mark that he had. After 3 minutes, he escapes from the pocket dimension, but upon being lifted out, he immediately has 0 health, and falls onto the ground.

Name: Skilled Rebel
Description: Half-life oriented NPC. Can sprint (Increases speed by 50%, side-effect of losing 1 stamina / second and cannot work without stamina), roll (Increases speed by 50% for 1 second, but prevents him from moving for 0.5 seconds afterwards), and slide (Makes him slide, slowing down slowly but if he is going down a slope, he gains speed). He will use these abilities to avoid grenades, AR2 orbs, and to get behind cover. He can have 40 stamina at any given time, and at 0 health, he's knocked down. Related to being knocked down, 15 seconds after the latest bit of damage taken, he begins healing 1 health per second. When he gets up, he has to wait another 15 seconds to begin healing the rest of his health. He has an increased amount of health, increased from 40 to 100. He also can use suit batteries. If whoever he's following is full on suit power, he'll use one he finds on the field and gain 15 power, with a maximum of 15 power. Suit power drops his damage taken by 50%, and his power takes damage like unshielded health, dropping down to 0 power if he takes 15 damage in a single hit, even at 15 power.
No model link. Simply fit miniaturized Undeployed Manhacks on his shoulders and give him a CP mask.