AR + Sniper is probably the most versatile loadout to run with the majority of the game. Especially with a grenade launcher attachment. Sniping is fun, and the game empowers you to snipe with all the great spotting options. However, it isn't always ideal, and variety is good! The game lets you switch your loadout whenever you want, so it seems foolish to pass up that advantage. There are several situations in the game where you will have the time to plan and pick a loadout that best suits the situation.
For instance, any of the rebel ops missions where you have to breach and storm a building, be sure to swap out your sniper for a sub machine gun. Keep the AR as backup or hell, run two subs. That extra maneuverability makes a big difference and if you run silent, you won't piss off the guys in the floor above and below. Most ARs aren't quiet enough in buildings to not alert people on floors above and below you. P90 with 50 rounds by default is a great breaching/interior weapon. I normally keep an LMG in loud mode for my back up if shit hits the fan inside. Suppressive fire is not as obvious as a mechanic as in The Division, but you definitely keep enemies pinned behind cover. If their are heavies in the area, the guys with the shield icons, they tend to move crazy fast on you and being able to hold down a point of cover with an LMG is huge. The stopping power + the mag size gives it an advantage imo. So often the cause of my death is being hit by multiple enemies at once. I am not a dead eye, so spraying some lead down range that keeps two guys behind cover, while I target the third, saves my ass.
Another situation where I change loadouts is before a defend/hold the position situation. The rebel ops radio missions are always this, and a few story missions so far give you a little heads up to let you know a bunch of dudes are gonna descend on your position. I used to go HTI + AR with grenade launcher but with even one or two points in VHC destruction perk, LMGs fucking melt cars and helis. The switching on and off of the grenade launcher is really clunky and especially annoying when you ADS that you can easily forget if you are in grenade mode or AR mode. That and the delays when switching weapons or on and off grenade launcher has gotten me killed several times. For defending a position, it is LMG every time + a sub machine gun if I know I am going to be going in and out of a building or just an AR I like such as the Mk17. Without even letting off the trigger, you can go from taking down the ground forces moving on your position, to shooting the car with backup or the heli coming in.
I have not found a use for shotguns yet, but I don't have any of them other than the stubby shotgun which is worthless.
I think the HTI is the most important unlock. It does so much. Invaluable for taking out people behind walls, long range shots where you can'y guarantee a OHK head shot and of course blowing up generators and drone jammers.
I've also been enjoying using the G33 scope variants on ARs and not always running a sniper. The extra zoom is enough for me to pick off guard tower snipers as we get near an objective and I know at least two of my other squad mates are always running an SR1 or HTI. The G33 with russian red dot is pretty nice. Very minimal FOV obstruction, clear optics and nice versatility. That with the L85A2 have been money. Haven't touched my beloved Mk17 in two days. Oh yeah, the L85A2 has a 50 round upgrade and has solid handling and recoil control out of the box.
All of this points to the need for being able to save weapons loadouts. If I can swap between saved outfits, I should be able to do the same for loadouts. Mixing up your weapons in the game is fun, and it is great that you can do it anytime you want, but a little quality of life improvement like saving loadouts would go a long way.