I'm using Notched Whip. While it has the lowest AR it has bleed. I main hand a katana and sometimes off hand this whip, because it can keep building up bleed and it can't be parried. It's great against parry happy opponents.
Guardian's Tail has the biggest AR and does Poison too. It can be buffed with Rotten Resin for extra Poison build up, but I just hate it's looks and never use it.
If you use DMB, or SLB on a whip (not sure about Guardian's), the buff is NOT visible, unless you swing the thing. Meaning your opponent won't know what hit him. It doesn't work on Magic Weapon buffs, because they change the whips colour to blue.