Help, what do I buy!?

During the RP sale, I bought enough RP for Snow Day Bard and Dragon Trainer Tristana. I didn't know at the time, though, that SD Bard would be on sale upon release. So when the Poppy rework went live, I bought more RP to get Lollipoppy, not realizing I would've actually had enough left over for that.

That means I now have enough RP to buy one of the following:

• Sandstorm Ekko.
• Snow Day Malzahar.
• Winter Wonder Orianna.
• Volcanic Wukong.

Ekko and Wukong are my 3rd and 4th most played champions after Garen and Tahm Kench, and both of the skins on the list are my favorite skins for them so far. Sandstorm Ekko is only at 975 RP for a limited time though, isn't it? Malzahar I need to buy on this account first, meaning I'd have to save up 3500 more IP to get the skin. I haven't played nearly as much Orianna as the other 3, but she is one of the few mid laners I do play, and I'd like something to replace the TPA Orianna I got mystery gifting myself. Winter Wonder is her best skin, so it's hard to resist.

So, I can think of reasons why I should get each one, but can't decide! Help!