HC ownz. Actually, if u make 99lv HC char, that MEANS something. One small mistake, one lag and it's rip. That's cool and I'm fine with that.
PKs are OK as well. I didn't PK myself, but I find that an obvious part of Diablo. That is why I think D3 sux in terms of HC gameplay. No open PvP mode. TPPK was awful, but that required just one simple fix from Blizzard - implement a timer counting backwards from 10 to 0. When you declare hostility, the timer is displayed to all players, but PK is not yet hostile. When the timer reaches 0, hostility is active. That would give casual players enough time to either go into town or leave the game, while still make PK possible.