Either first or third probably. I wouldn't really build it if you need Rylai's (which is most games), because it slows your utility but gives you ult CDR+lane sustain. I could see a Rylais -> Liandry's -> Malignance path but Malignance =-> Liandrys/Rylais (either depending) is also doable.

Honestly not a terrible item by any means on brand, but it makes you squishier and reduces your main slow/HP shred timer. If you get it third, it's only because you don't need Orb, Zhonya's, or Cryptbloom. Has a place but not often imo