The latter two are especially good for psychopath fights since they can't be dropped accidentally. For general everyday zombie killing, the best combo weapons are the nailbat (simply because of how easy it is to make), defiler, tenderisers and knifegloves.You can still make a weapon without having its combo card, but you will only get half the PP per kill and won't be able to use its special move.For example, there's a poster near the coffee shop where you emerge from the safehouse exit. You get most of the combo cards by levelling up, but some are acquired after certain psychopath battles or survivor escorts, and others can be acquired by looking at movie posters around Fortune City.You also get PP for every kill - the amount varies between weapons but usually you get more PP for sillier kills. Usually they're far and away more effective than melee weapons you can just pick up. Use the combo weapons as much as you can.