I'd say Yeti only because Coco's are but a substitute and the Law of Substitution states that when the original goes down the substitute does as well; that is to say that until the Kiki rises ( which may never occur due to a perfectly viable and somewhat more appealing substitute ) the Coco is not supposed to rise at all.
The yeti, as far as I know, is not a substitute for anything at the moment though there are similarities to them but only through the fact that they are plushies; plushies in general should rise in price towards the end of December and everything will lower towards Christmas.
Holidays are perfect for buying and selling; my advice, by Yeti's since they are cheaper, easier to attain, and if anything goes wrong such as a massive unforseen disinterest in the item you can sell them for more individually than Coco's since the drop really can't be that much due to their already being a lower priced item.
Then again, I don't know all that much eh?
