Its kind of clear that -hate cloak is for raiding and the other one is for PVE/Solo PVE/PVP.
In raids assassin pulling aggro usually means instant death so as Civilix wrote you need to stack up -hate. If you don't have enough passive -hate you will be aggro magnet and spend most of the fight "waiting out" aggro.
For group dungeons you can get away with lots more damage and occasionally drop ball on aggro pulling (as the fights are shorter than raid fights you can manage aggro better via feats/AA)so Slayers cloak can be considered.
For solo pve you can stack Slayers cloak with hyrkanian daggers, jiang shi ring and relish in death feat and get pretty sick amount of fatality chance so you are tearing through mobs like a beast. Not only its super effective (fatality animation does AOE damage, makes you immiune to damage and gives you 20% dmg buff) but also is just rad.
In PVP Slayers cloak is next best thing to dedicated DPS PVP T3 cloak.
So to anwser your question about cloaks: get both over time.