Title.

Hobbit Sagas or Khaza-dum? I play semi-progressively by the way, I use all the cards in the cycle right away to play its corresponding APs.

Khazad-dum, if you ask me. The quests are much better. You can build a good dwarf deck with either, but Dwarrowdelf also has quite a few other powerful cards, while the Hobbit boxes are extremely dwarf focused in terms of player cards.

I'd say "get whatever you can get your hands on", as a lot of the earlier card pool is sometimes out of print. Khazad-Dum should be easy to find, though the APs might be more difficult to track down. The Hobbit boxes are nice, but the quests are really weird and most of the cards favour Dwarf-decks. If that is what you like, then go for those, but otherwise stick with the KD Deluxe (which also has Dwarves, early card pool was filled with the hairy buggers) but gives access to Noldor and other good stuff later.