I really like the cool, sleek look of Suicune, it just looks so graceful. The other two are pretty awesome as well, but I think I like Suicune a little more.
I like Suicune and Raikou equally actually, which is something I never thought I'd say because I never thought I'd really grow to like Raikou much! Buuut if I had to pick one, it would still be Suicune.
I like Raikou, though somehow I think that's mostly because it wasn't a central part of one of the movies. I felt bad for Raikou and felt like he needed more love, and he's become my new favorite of the three.
Suicune is my choice because he is a defensive beast (sorry for the play on words XD) and also because his design is the best of dem all
Ignoring the fact that Suicune got a part in a movie and a whole game based on it, I'd say my favorite is Suicune. I love its design and the idea that it can walk on walker like its made of ice. Suicune has far more of an air of mysticism to it than any other of the beasts and I think that's in part from its design. Even if Suicune isn't the best out of the bunch for fighting, I'll always like it the best.
Mine was always entei because of the raw power, it's fire type, and it just has a look that commands respect. Other than that catching it was a true way to show your skill when I was a kid.
Suicune! It's not even a surprise why so many people like it. It was marketed extremely heavily, especially in Pokémon Crystal and subsequently HGSS. Plus, the Celebi movie definitely helped. The design is also A+. It looks absolutely majestic.