you cant compare them, they are totaly different weapons
asw is ment for penetration purposes, much like tpg, basicaly you buy asw or tpg at low rank and later you buy frf2
frf2 has more flexibility, since you dont even need to quickswitch and it comes with 10 bullets, while ASW comes with silencer and can wallbang nicely, mosin is the run and gun type of weapon and if anything you could compare it to blaser and dsr-1 where it might be slower but is a lot more reliable in 1 hit killing
as for shotguns, similar can be said, striker12 is easier with good refire rate, great for spamming,m great CQC weapon dominates 0-5 meters, can clear whole small room, blue skull on the other hand is a beast at all ranges, its a true 1 huit kill weapon that is so OP due to even have amazing ranged abilities
if you completey suck or find 3+ enemies at 0-5 meters then striker12 is better, othervise blue skull is godlike, best PM weapon by far, surpassing DM (again unless you completely suck)
Why do Zombies want your Brains? Because you do not use them anyway!