I really don't like HFC. Far too many AoE all around which heavily detract from the actually fun mechanics.
And between HM and BRF, BRF was bigger and more varied, so I'd say BRF.
Blackrock Foundry goes down as one of the worst designed raids of all time in my eyes. So much goddamn blacks and reds and browns, nothing but orcs and generic boss mechanics mashed together in some sort of annoying and bland way. Environment has a lot to do with this opinion and BRF had to have the blandest possible.