For you, we are not talking about OP equipment, but the one that for you depending on each class and campaign, what weapons would you recommend to use?
The question is so wide ranged, I don’t know how to answer that properly, but I give it a try:
Engineers can carry bolt action rifles and grenade pouches as they can build ammo crates. But stick with the campaign. Sometimes ammo pouches and full auto or meta guns are better (Berlin, Normandy).
All classes that can’t carry ammo pouches:
Stick with early or middle game equipment. FGII, AVT, AVS or M2 carbines aren’t the good choice. You run out of ammo quick. Specially with flamethrowers. Don’t depend on teammates building ammo crates for you, that’s my device.
AVT-40 by far is the best rifle gun.
LAD is the best smg gun
LMG? Eh it’s preference.
Depends on where you are playing.
Use MP38.
Mp38 will be spammed once war thunder takes over.
Cheap. Precise (because) good all rounder. Will allow matching out of sweat turds spamming select rifles, fedov stg and m2.
Best axis smg to still play casually.
Nah, Kurz is better 
Conders MG,g43 Kurz, stg, stg sniper, mg42 early, mg45,
m2 carbine, Fedorov, A6 MG, Pps42, mkb, mkb sniper, avs, avt…
Vg1-5
.
0/10 list, no artillery luger or m1 carbine
There is no super equipment with incredible abilities in this game.
The basic infantry rifle deals some of the highest damage with the highest accuracy.
Phosphor grenades deal damage to both enemies and allies.
Semi-automatic rifles have reduced accuracy and damage of 60% of the damage of bolt-action rifles even though they have the same caliber.
Intermediate carbines do 15% more damage than submachine guns.
Any weapon is OP for you. In closed beta tests, ppsh with a drum magazine guaranteed 72 frags without reloading. And this is realism.