WTB chaos axe but need some help with a few questions

I was just wondering, I have a battlepick ATM and this is piercing dmg, but I'd like to get a chaos axe which is slashing.. was wondering what the difference is between piercing and slashing if there is any, and which one would be better overall for tanking? Please let me know, either in reply here or my name on game Jade Lynne. Thanks!

Basicly different skills and equipments defend against different kinds of dmg, thats about it.