I'll echo what the others have said. AV and to a lesser degree IoC. Expect to die some in the latter but if you go to the docks and heal people and manage to stay alive for awhile, you can get a decent number of HKs.
I don't recommend random queueing BGs, if you are not experienced with PvP and using your entire toolkit to protect yourself and stay alive. In smaller settings regular PvPers will focus you and eat you alive every time you rez, and in random BGs nobody will protect you at all. They'll just yell at you for not healing them (while you're dead).
Also doing the hidden requirements seem to be character wide. I've been progressing as MM with the hidden artifact, and if I swap to BM I have the hidden skin 1000HK/200WQ unlocked on it as well despite never having completed a single WQ/earned a HK as BM.
Hah, had same thing... after a few xavius wipes, I had +150 kills on the progress bar. Greatly amused.
It's actually easier than doing it as DPS...
Just stay at a distance and heal... while DPS will lose out on honorable kills while "corpserunning", healers won't if they stay at a reasonable distance.
Should be a perfect timing with the current weekly event to do too...
Anybody know if you can transmog your hidden artefact skin and still get credit for this?
If alliance, do Ashran. If Horde, AV might be better option. Only landed in 1 good Horde ashran at 110 and it was a Goon Squad premade to stomp Swifty lmao