Hmn, that’s really up to you, there are hundreds just on this forum, and more in books commonly recommended for baneful magick. Try the search at top right with the search strong “death curse” and have a browse through some of the options, see if something stands out for you.
What you choose to use should fit your energy and your cultural preferences. You have a lot of options and you should research well before you choose.
I recommend E.A. Koetting’s book Baneful Magick as a good primer on the various currents that approach cursing in various ways. I hear the book Magickal Attack is good, I see it recommended a lot, but I have not tried it myself.
Personally, I have a goto binding I always use that combines Vovin’s freeze spell and poppet magick:
For death curses it varies, I have an elixir I made under direction of Azrael that I use on a poppet, but I don’t recommend it as it takes a lot of time and effort to produce, and after it’s worked for a while I burn the poppet and bury the ashes.
Maybe try this one: