Wee Beasties

So while I'm working on the current projects, I'll also be working on a few side ones. Now, putting aside Lord Corrupticus Fellwing and Twinkle (I'll share more on who, or rather what, that is soon) I want to start working on some monsters. There are a few idea's like a Storm Dragon and a Giant Spawn of Tzeentch, but there are a few other creature's from my stories I'd like to create like Nightmare Fiends, various Trolls, etc. My only problem, which one to start first?