C41 is definitely the best, by far - excellent primary weapon (KEK-10), gives you Spares (which is great since the KEK-10 does run out of ammo fast) and Lock On (which is excellent for your turret), and the best secondary (M9).
SM82 is okay - you get a good-ish primary (SMG-9) and gives you Tough and Steady (which is good for the turret but not as useful as Lock On). But I would take the C41 loadout over it any day.
BL81 is also okay - you get a fairly average primary (Blishlok) but you get both Lock On and Steady for your turret, which does make it into a pretty good powerhouse. When you use Bushwhacker it’s important to ‘repair’ your turret by picking it up and quickly replacing it, and Steady often allows it to survive that extra second so that you can grab it before it gets taken out by someone who is popping in and out. I’m a little on the fence with this one, since the Blishlok is fairly inconsistent, but it does allow you to rely on your turret a little more than usual. But, remember, if you’re going to use BL81 you have to make sure that you place your turret in good locations and that you constantly ‘repair’ it whenever possible because you are relying on that thing a lot more than you would with C41 or SM82.
So yeah, C41 is the best but both SM82 and BL81 are still perfectly usable.