BK does his job well without limit breaking, i personally limit breaks offensive heroes that do damages, but queen of hearts a bit underwhelming, so maybe BK then
I have neither so I can’t say from first-hand. But Queen of Hearts cannot be dispelled like BK can and that can get annoying when facing her, especially in Equalizer.
After facing a ton of both of them, BK is the much more challenging hero to face. Don’t have either but people seem to prefer attacking with BK over the queen as well.
I have BK - not limit broken though, because I prefer to do it with the heroes that do damage. While I have found the Queen annoying on defense being immune to dispell (well, not immune per se, but the taunt is per minion and not as a buff), I don’t really imagine taking her on offense over BK (as @Chadmo says)
He is simply much sturdier and his attack up great.
Personally, I would wait with my aethers for a strong hitter. But if you want to choose:
for offense definitely BK
for defense tank position I think I would prioritize BK
I agree with waiting for a hitter, but if you want to LB one of the two, I think QoH (and her taunt minions) will benefit much more from the increased stats than BK.
There seem to be a lot of dispelling options available these days - I am leaning towards Queen of Hearts because of it. But we all know we are fighting against the board more so than the tank, in some cases! Both great choices though - good luck