What to use credits for?

I have 6 credits to use. I guess the best thing to use them for is 2 trilogies and was pondering between these.

The Green Bone Saga - Fonda Lee

Gentleman Bastards Sequence - Scott Lynch

Memory, Sorrow and Thorne - Tad Williams

The Bloodsworn Trilogy - John Gwynne

The Broken Earth - N.K. Jemisin

The First Law Trilogy - Joe Abercrombie

I know there are sales so does any of these go on Sale often that it may worth it to buy some with credits and others on sale?