Mastermind

Medic
Combat Medic is a base damage reduction while reviving teammates and is really only helpful to getting further skills. Quick Fix decreases the deployment time for first aid kits which can come in handy. Uppers (Ace), the main reason for this skill tree, adds a total of 10 extra first aid kits to your inventory. Further, they are auto used on downed allies within 5m.
Controller
A huge survivability boost, this skill tree is indispensable. Forced Friendship increases cable tie count, and tying speed on hostages. Joker is where your survivability starts. Able to convert non-special enemies to fight for you. Confident (Ace) Increases the power and range of your intimidation, and can you now convert 2 enemies at the same time. This is particularly helpful since we rely on our range to deal with enemies. Partners in Crime (Ace), while having a converted enemy, it increases your movement speed, increases your health, and your converted enemy takes 99% less damage. Hostage Taker (Ace) is another huge increase to you, while having a hostage, or converted enemy, regen health every 5 seconds passively. This skill tree is amazing for group or solo games alike.
Sharpshooter
Stable Shot is a base increase to weapon stability. Rifleman increases the snap zoom speed by 2x. Marksman (Ace) increases accuracy for all SMG/AR and Sniper rifles. You will also gain a 20% accuracy bonus while aiming. Aggressive Reload (Ace) Increase your reload speed with SMG/AR and Sniper Rifle. Any kills with headshots increases your reload speed by 2x. Graze (Ace) hitting your target will deal 20% of the damage dealt in a 1m radius around it’s trajectory. It the bullet would headshot kill, increase the damage deal to 100% around the bullet trajectory.