by Thanee
The small expansion packs have one adventure and a handful of new player cards.The deluxe expansion (Khazad-dum) adds quite a bit to the game and is a good starting point. It has a bit of a dwarf focus, so if you like dwarves, you cannot go wrong here.
You also need it to play the Dwarrowdelf cycle adventures.
Of course, you could also just buy the expansions in order (i.e. start with the Mirkwood cycle).
Overall, however, the Dwarrowdelf cycle adds a bit more to the game, so if you want to keep your spending a little lower, I would probably get Khazad-dum and then pick some of the Dwarrowdelf cycle for starters.
Bye
Thanee