This XpresSpa panda neck pillow is by far the most comfortable one I've ever used. It's filled with microbeads that conform to your neck shape while the pillow itself remains firm. This is more overstuffed than other neck pillows I've seen and I thought it was a little too stiff at first (like a furry neckbrace), but after reclining my seat a bit the firmness was perfect. No more stiff neck on flights! Not to mention it's adorable and the top is velour-soft.
XpresSpa has other cute animals too (pig, bear, dolphin), as well as regular neck pillows without animals. Traveler's best friend!
*Panda photo is mine. Other animal travel pillow images from XpresSpa site.