Use it if you've got it, but if you're making it I recommend just sticking with the standard. The damage buff really isn't worth it and all you'll end up with a muddled ammo chest. You might try using up the regular to get rid of it, but the game will always give you more. And when you use the AP/HP you won't really notice the difference, in my opinion. I think the dev's could do more to differentiate the rounds.
Standard Ammo - enough said.
Magnum Rounds - increased damage, more recoil.
Explosive Rounds - massive damage, slower fire rate.
Incendiary Rounds - trades damage to chain-ignite zombies.
Electrical Rounds - trades damage to chain-shock zombies.
Flechette Rounds - trades damage to penetrates armour.
Rubber Bullets - any shot you miss rebounds and bounces all over the place until it hits something (including you).
Boomerang Rounds - yeah ... never fire these.