I play engineer most of the time because I get frustrated that no one ****ing buffs! I would love to be a solider all the time but its just not feasible when no one buffs the guns!
what is your main class and why
Current main class is Operative. Simply because I’m having fun using it.
A very close second is Medic. If the game keeps me playing for long enough, I’ll have four characters all maxed per class.
UAV is pretty epic. I respec’d all my dudes…and I am not ashamed to say most now have the UAV as an ability. A tactical toy and a bomb. yay. 
Because I nearly always change to an operative to get a hack portion done, and am very good at getting’er done, I make sure to load up on essential base Operative abilities like caltrops, EMP, sticky and or UAV. And Spotting if I have enough points. Many maps my team has lost, I didn’t change to the Objective class. Most of the times we win, I was one of the objective class. So, it has become part of all my builds to have Operative so I can switch and be effective. 
Soldier class. I find the responsibility of that class simple; Shoot bad guys, give ammo to buddies, plant bombs. I admit, (poorly)played many times as a medic, I’m not quick on my reflexes so I try to compensate for my shortcoming by being straightforward. A soldier. 
Operative and Part-time medic when all other medics slacking off.
I really hate to see people who play medic fail their job… it’s the game changer thing D:
But my main class is Operative because there’s so many stuff to do as an operative and it doesn’t require 100% markmanship, require lots of tactics too.
Engineer Operative Medic Hybrid. FTW! I come up 1 ability point short of perfection, lol. 