Update 5:
Rapid Fire / Spike Traps / Caltrops / Sentry -T6 PTR
This is a weird one, its viable for high level play but its very slow. Note I do not have the new RF bow and used M4 to make it work. Sucks on single targets, but good on packs. Finished T6 bounties without much of a fuss but I wouldn't put it at T6 viability. It's above strafe but nowhere near EA/MS/FoK.

Update 4:
Immolation Arrow/Buriza - T6 PTR
If you thought frost arrow was purpose-build for Burizza, this skill owns it. 1245% to 3 targets in a mob, with 945% AoE. Good size projectile too. This is my fastest clear yet and ahead of MS: Arsenal/FoK with none of the regen-issues. Note: Currently, DoT interaction with RD means near instant-death. Until they fix it, use it at your own risk.

Update 3:
Bola/FoK - T5 PTR
FoK is without a doubt, the closest in terms of clear-speed to CA/MS. Bola in this case, helps to save and regen hatred. Combined with Buriza, it gives your FoK dive-bombs another 1-2 FoKs worth of damage when you make all the bolas explode at once. As of now, it is possible to destroy an elite pack with less than 1 globe of hatred. Will redo in T6 once I get some FoK% and Holypoint quiver.

Update 2:
Strafe/FoK - T5 PTR
Without question the slowest spender. However, throwing on old Sash of Knives + FoK and dive-bombing mobs brought it up to speed with multishot. Please decide whether you want Strafe to be mobility (make it cheaper) or spender (increase damage and cost per time), and adjust accordingly.

Update 1:
Multishot bounty farming - T6 Live
Surprisingly, MS:Arsenal with ambush is still almost a 1-shot crit on smaller mobs. Haven't bothered trying rifts. With double Unity/Aughilds/Smoke Screen, surviving T6 shouldn't be too much of an issue. Chakram is too annoying with all the running you have to do on T6. No leet kiting skills here. Also, still not using M4.