Depends on who your fighting, if your opponent is melee, it ichor would be very nice cause otherwise your damage will be horrible. Confusion could be very good, but you can't count on your opponent not having immunity. Venom is just plain better than fire, shadow, frost, poison and cursed, so they entirely depend on what's available to you. I'd say see if confused works before each battle, and if it does apply that and then apply ichor or venom. If you can try to inflict multiple debuffs.
I don't think debuffs can be applied to other players in PvP.
For PvE, Ichor is better than Venom if you're hitting roughly four times a second (7-8 damage per hit vs 30 flat DPS), which is harder to do for each enemy in a crowd so Venom could be better.
About 70% of enemies are immune to Confusion so that's garbo.
Cursed bullets work in PVP, which makes it the easiest debuff to inflict. Ichor bullets work too but that debuff isn’t as powerful for obvious reasons. (I actually did test a large variety of weapons specifically for a similar question to this a while back). Iirc venom is completely unable to be inflicted, though that may have changed in 1.4.1.
wow, okay. no flasks worked before.The flask and bullets work now.
also player-based shadowflame doesn't exist