Match history
Karma full support is what works best for me. After the Rylais rework you don't really need it anymore. The only real addition it gives you now, is the slow on your W to make it finish your cast easier. However you can also achieve this if you build a Talisman of Ascension OR Frost Queen's Claim.
You could also consider building a Rod of Ages for the mana & health pool, and the AP is nice too.
Of course Abyssal Scepter is also very good on karma, as it helps your AP teammates to deal extra damage as well.
Liandry's Torment is good to peel with, however I'm not a real fan of full AP Karma. This is a personal preference.