Every person requires a different tactic. Mine is maxed hero shield and leg-it, one IEG and the rest keg.(though thinking of putting some at FF, depending on the slow effect of shield after update.) But like I said, every person requires a different tactic. You should experiment with abilities until you find what suits your playstyle best.
I've been playing my commando for a long time and is now trying out gunner. It's fun, but very slow compared to the commando. I'm only lvl 9 as a gunner and my build is like this: shield1,IEG1 and Legit3. Tried FF and feels it didnt make a difference. As a gunner it's those pesky commandos I have to watch out for as it's slow to strafe and dodge. I'm going to try these tactics that u guys have posted. Keep up the good work!
I suggest that after hero shield you go for leg-it. Those two are the two abilities I use most, cause they are the most useful. But once update kicks in I suggest you also grab one point in keg, cause enemy-slowed+You leg-it = enemy stands there and watches as you run in circles around them massacring them completely.