Well, I don't know... I like them all. Lugia really appealed to me because I thought that it looked so neat and pretty. The whole design of it was original, and different. I liked all of its colors, and its song was really pretty. I loved watching that scene on Pokemon the Movie 2000 where it was swimming in the ocean, and you could hear its song. I didn't like, though, on the Pokemon Johto episodes where Ash and them found Silver and its mom, but they didn't really sound like the Lugia on the movie. And I thought that there was only one, anyways? You could tell those episodes were just fillers...
Articuno is also another one of my favorites! I think it's a really beautiful Pokemon. ^_^; Suicune was my favorite legendary dog, and Mew, Celebi, Latias, and Jirachi were all cute. I also liked Mewtwo's design. He was really cool-looking.