I rather liked some of the unique material and PrC's presented in HoHF, so that would be my vote. But to be fair, I also liked the Quintessential book and haven't read through H&H.
I would say it depends on whether you are approaching it as a player or a DM.
If you are a player, you can't go wrong with Heroes of High Favor. It's written with players in mind and will give you lots of ideas-- in addition to all the crunch.
If you are a DM, and you are looking for background material and help in expanding the role of dwarves in your campaign, then I happily recommend Hammer and Helm.
(AND Heroes of High Favor. But I might be biased... )
Heck, if you have $20 to spend, then I'd recommend HOHF Dwarves AND either Half-Orcs or Elves. But again...