Estus, ugh, for PvP? Well, certainly not if you invade, and hopefully not when you're invaded unless they humanity heal spam first. Considering you can get 10 Humanity in 10 minutes from the PvP, there's no real reason to estus even if you're the host anymore.
I'd go: Humanity Green Grass Loyd's Talisman Poison/Lightning Resin/your choice if not going to buff. Your choice (moss) or nothing.
Nothing is actually a valid option if you want a microsecond less of scrolling time through the items. Not to mention poison does so little damage that using moss on it can actually give the opponent too much time, and few people use poison anyway.
I always keep on estus, a summoning soapstone or invasion eye, and either a dried finger, grass or homeward bones. If I'm forest invading, I like to add Lloyd's talismans and sometimes dung pies. I basically always keep on a healing item and an incompatible online play item, for the wtf shrug, even in offline mode.
If you're going to chug estus in PvP: 1.) You're doing PvP wrong 2.) Humanity fully restores your health while Estus doesn't anyway. 3.) If you invade, your only (well, primary non-limited) way to heal against a healing opponent is Humanity anyway, so you should probably farm some humanity anyway. 4.) I got 99 Humanity by the end of my NG without even farming. Though I did die on the way and against Manus once or twice, and explored the Abyss on 2 separate occasions, so I killed quite a few of those dark things. But even then, I never went there to intentionally farm.
The real pain in the ass farming comes in the form of Gold Resin, which also happens to be the best item-related buff.