I feel like Raikou doesn't get enough love, so that's who I'm going to pick. Entai is like Flareon in my eyes but Suicune is still pretty cool on it's own but I think it got some attention in the anime if I remember correctly.
Suicune is probably the best, but I have to admit that Entei is quite the badass. It's very regal, like a king, whereas Suicune has a sort of serenity to it that makes it beautiful. I really don't care much for Raikou though.