Every thing with -40% vertical recoil perk?
Or maybe every thing -30% horizontal recoil perk?
Or maybe a little mix like automatique and smg => vertical and LMG => horizontal?
I got the feeling this one is better with horizontal:
I tend to go vertical every single one and horizontal on thommy guns just because.
If somehow the game gives me horizontal befor a vertical roll on a gun besides thompsons I get It and keep it.
Every soldier I go vitality, recoil and run speed. Even engineers with garands have it, I rather have the soldier equiped now with them even with no actual use and change the weapon to another one latter that works with that perk and start over again latter.
Generally speaking, I tend to take all firearms to the range, video it, and slow it down so I can see which plane it is bouncing on more, and use that as the factor in determining which skill to add.
Same, I have a trooper/assaulter/mg guys with only the hori perk and another with just vert perk, so when I get a new gun I equip both with it and see which perk is better for me.
Generally I take horizontal on anything automatic and vertical on anything semi automatic. The one exception being automatic rifles, many of which I prefer with vertical reduction.
H for anything with H > or = V. So German MGs, M1919A6, Tommy w/ drum, Sten. Also testing on a few select weapons with H >10 where it feels nice. Vertical is the go to for everything else tho.
P.S. on the AS-44 and Stg-45(M) squads you can get both so you have basically no recoil.