Val: Utility Medic
Laz: Not a medic. A reviver.
Caira: A straight up medic
Slim: Combat Medic
Caira is the hardest to down someone mostly because she heals so well, and so many at one time. The bright side is that she doesn’t have tranqa, weakpoints, or spore clouds to annoy you more. Just heals, a little fire, and a speed boost.
Slim is mostly a combat medic. He’ll be mainly damaging you while healing people. It’s a lot easier to down someone with a slim, but he’ll always be doing damage to you when not using spore clouds and heal bugs togeather for clutch heals.
So all in all, Caira is harder to down someone, but Slim is harder to down someone without a ton of damage from everyone on the team.