“My playstyle: Rush in, kill people, do the objective. Which would be the best?”
Personally, I think you might prefer Fletcher more. It’ll take some practise to master throwing the sticky granades; whether it is at live targets or at the walls as traps, and finally when to detonate. (By clicking or shooting at your own granades, whichever is easier considering the situation.)
Thus, when you have mastered the merc: You can easily rush in, kill people, and do the objective. (Being an engineer means you will be able to plant the C4 or fix the EV well before the next enemy wave gets back to you and the objective.)
And yeah, I have seen Fletchers demolish entire teams on their own.
As for loadouts;
I am looking at ‘H63 Standard Close Assault’ with special interest. The reason is mainly because of the Augments that allow you to reload while sprinting (I love it on my Proxy), faster reload time, and the damage reduction from explosives (your own granades, mines, and other explosives).
Not to mention that as you intend to rush in, which means getting close up and personal with the enemy. Hence shotguns might be your weapon of choice, and with your mobility and reload speed, I think you should be able to keep on shooting and possibly even flank around your opponents.
The downside to this loadout is range. And if you just cannot use a shotgun, (I am one those individuals), then you might want to look at: ‘BL33 Standard Operative’ loadout. It is not as ideal, but the Quick Draw augment means you can switch faster between all your weapons; throw granades and then follow up with ‘SMG’ bursts of fire. The faster health generation kind of makes sure that you will be at full health when the next enemy wave arrives. And I guess it is little bit handy to avoid the fall damage occasionally. (Mostly in the Terminal map I guess.)
But… please take this suggestion with a grain of salt. My personal experience with Fletcher is very limited as I prefer Nader. (Granade launcher comes with a rather long firing range.) But were I to get serious with Fletcher, I would choose between those two loadouts.