Creatures are cool and often have fun abilities and amazing art, but of all the spell types, I feel like there is a larger fraction of creatures that rarely/never see play than any other spell type, so I'd fear we might get a spoiler that sounds cool in a Timmy/Johnny way but really isn't all that good. See previous expansion spoilers, like Talos, Sersiryx, Sardonyx, Skeelax, ... pretty much any legendary creature with unnecessary y's and/or x's in its name.
I'd go with an equipment, with the caveat that it not be an existing promo (e.g. I'd be shocked if Leviathan Scale Armor wasn't in the set, and the Spiked Buckler and Spiked Armor are likely, too, as might be Vorpal Blade, Leather Belt and others).