I tried all of them
Corsair3 > Pretty much pardoner buff + enchant fire + lv15 Cafrisun Set to maximizing the pillaging buff. (manahas difficult to get, so you have low def and chuck a lot of Pots and you can’t swash buckling too much mobs) . It kill quite slow, but you have most likely 2 drop chances per kill (1 from pillage success rate, 1 from kill drop rate)
Thauma2-Featherfoot2 > You kill slower because Joint Penalty have 22s cooldown, but you have 2 drops per kill. It always very boring to wait for the JP cooldown.
SR3 > You kill really fast with mobility, but need some good investment on your pistol, or rely on pardoner+enchant scroll+manahas set like corsair 3 to farm.
And recently I found another build which could be as good as SR3 without much investment,
which is base on Sorcerer, I currently testing 2 sorcerer mats farming build, marnox is best, but you can use helga/templeshooter/cyclops/netherbovine just fine, i did well with +11 T0 windia rod.
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Cryo3-Sorcerer3-Sage (i think cryo3-sorcer2-linker1-sage prolly better)
In open map, I saved 6 warp points different area in the same map, whenever I cleared 1 area, i use open portal directly to different area. Which I usually found that mobs spawn slower than what I cleared in entire map. But this trick cannot be use in dungeon like Hunting Ground.
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Linker2-Chrono3-Sorcerer
Start from R8, the rank slot is precious so i’m not recommend this as sorc need c2 to be good which also waste up R9 in future. But as farmer build, this is quite fun, you already know what to do with this build.
But finally, what I found is my best drop run is to have Corsair3 alternate afk in another computer, while you use SR3 as your playing character. 
)