Assault
Assault is the most all rounded class with 150 health and some really good weapons. I recommend the last gun with no recoil as it does tons of damage to the head. I also recommend the cr-2 if you are not as good at aiming as it does a lot of damage with body shots but you need to be at close to medium range for it to be effective. Ability wise You have the scatter gun which is incredibly powerful at flanking enemies and killing heroes. This can 1-shot any troop, so you can get behind enemies and take them out 1 by 1 without the rest realising. This also does a lot of damage to heroes, so if you see one, use it. It also gives you a speed boost, so you can use it to get back into a fight or at the start of a match to get to the objective first. Assault also has a thermal detonator grenade which is probably the best grenade. You can get some good multi kills with this by chucking it into a choke point or a group of enemies. Try and place it on an enemy that won't notice or can't get out of the way like an explosive sentry or a scoped in hero. You can also use this as an escape by throwing it below you and running past you, potentially killing any chasing enemies. The last ability is your choice with star cards, but I recommend the toughen up ability, as you can easily get back into the fight by instantly regenerating health in cover or you could use it before a fight so if you get hit, you will regenerate your damaged health. The default ability is the scan dart which allows you to see enemies through walls. Use this to know where enemies are, so you can throw in a thermal detonator or wait until they come around the corner and kill them.