Buck may try to stomp on you and scare you with his high health pool and regen. Just remember that Buck has a pitiful damage output, start on him early. If you are at or below 700 health, use an escape to regenerate. A clever Buck is deadly.
Maeve is probably the safest pick against Raum, cause its hard for him to hit you. He also has high damage-falloff, you don't, so you can use that to your advantage and keep your distance.
STUN STUN STUN... when with allies stunning anyone without a shield (excluding portable shield like tarvold's) can be your priority to help your teammates clear the point