Technically, Critical Hit Lv. 3 deals more damage as criticals deal triple damage. However, the only firearms that actually benefit from Critical Hit Lv. 3 are sniper rifles and magnums as their initial critical hit rate is far higher then any other weapon type. Critical Hit Lv. 3 raises your critical chance by 50% (I believe) but one thing to note is that it does not add a 50% overall likelihood of performing a critical hit, but rather it takes the default weapons critical chance rate and increases it by 50% (example Leon's Wing Shooter handguns have a initial critical hit rate of 8%. If your equip Critical Hit Lv. 3, it raises to 12% as opposed to 58% due to the initial critical rate being increased by 50%). In short, I'd stick with J'avo Killer Lv. 2, a 50% damage boost to all guns is pretty sweet.
When facing a zombie apocalypse, don't join up with a group. Why? Because you'll end up blowing your own head off due to all the pointless drama caused within.