I will always be partial to the T-Rex and velociraptor. Blame Jurassic Park, but they're still my favorite dinosaurs of all time.
But I have a soft spot for all dinosaurs, ever since I was a kid. Hell, I even wanted to become a paleontologist when I was like, 6. Still do, too, just a little bit.
But for real it's probably Triceratops because it's essentially a cow with a shield and three big ruddy horns and if they were real one would be my best buddy and I'd ride it to work.