Which edition should I buy?

[Down Cast]

I'm seeing master edition and deluxe edition, but don't know if I will be my money's worth.

[lexilogo]

Deluxe is the regular edition bundled in with Iceborne, which is probably your money's worth you want. I believe Master's Edition includes a couple of extra cosmetics but that's about it.

[Sir Cheddington]

Deluxe = Iceborne DLC + (Deluxe) cosmetic kit DLC <----- Useless without base game

Master = Base game + Iceborne DLC

Master Deluxe = Base game + Iceborne DLC + (Deluxe) cosmetic kit DLC

Master editions is for when you do not have the base game
Iceborne basically doubles the content of base game

Best value for money IMO will be the master edition, (I personally haven't used any of the stuff I got from the deluxe kit, but feel free to check it out: https://store.steampowered.com/app/1118012/Monster_Hunter_World_Iceborne_Deluxe_Kit/)