I was at a museum with my son when I saw the breaking news on my phone. I kept seeing people high five each other, and hugging each other, saying things like "He's guilty!" or "They did it!".
So many cool ones to choose from, but I'm now 40something, and ever since I learned about Dinosaurs in the late 80's, triceratops has always bee up there. My top 3 has changed a bit over the years, but the fact that triceratops has consistently been high up makes me conclude that I might as well consider that to be my favorite.
Besides, it's like a Rhinoceros but with even more of the cool bits.
Archaeropteryx is also pretty cool if that counts.
But my favorite prehistoric being has to be the trilobite. Cambrian creatures are so fascinating.