From my experience so far from Beta..
My favorite 3 guns are the LMG with 404 dmg 8 rof, and the auto shotgun 808 dmg that fire grenades for aoe those damn bugs, great for killing those armored warrior hellbug. Favorite AR is the 375 dmg with 3 rds burst 30rd mag, put a scope on it and you kill things so fast, extremely accurate, double tap and kill most things.
I like fast bolt action sniper rifle. The pistol with 4x crit dmg, head shot hits like a truck. BMGs are pretty much all the same...none are significantly different than another. Infectors seem too weak, I didn't use it much. Grenade and rocket launchers seems to be a bit weak, should be able to 1 shot most regular mobs, and the small ammo pools didn't help. SMG chew up my LMG ammo so I don't use it, too weak...I get annoyed using them.
Best shield has to be the shortest delay Spark shield regeneration with bonus 25% hp regen. Grenades I like the flash and frag the most.
The rest of the other guns are meh...We need laser and plasma alien guns that regenerate ammo or a perk that constantly regen ammo.