Lugia and Ho-oh
Lugia and Ho-oh made their debut as two main legendaries in Pokemon Gold and Silver Versions. Lugia could be found deep within the Whirl Islands (interestingly enough, Lugia is Psychic/Flying-type rather than Water/Flying) and Ho-oh could be found at the top of Tin Tower (known as Bell Tower in fourth generation). Lugia is the more defensive of the two, while Ho-oh boasts strong offensive stats. Both of them belong in the Uber tier, but Lugia tends to be more popular due to Ho-oh's unfortunate quadruple weakness to Stealth Rock (he loses 50% of his max HP just from switching into Stealth Rock).
Ok, let me be honest: I'm not actually all that fond of Ho-oh. I just couldn't take him very seriously after I realized that his tail looked like a Voltorb exploded in it. (Plus he just looks so angry all the time! Although I suppose if a Voltorb exploded in my butt, I would be quite displeased as well.) I much prefer Lugia (in fact, he shares the title of being my favorite legendary Pokemon with Mewtwo) because I love his sleek and almost dragon-like design. However, Lugia and Ho-oh together make up my favorite "titular" legendary pair (e.g., Groudon and Kyogre, Dialga and Palkia, Zekrom and Reshiram) because I personally think they have the best design and complement each other very well. In short, I love their duality. As a result of this, I enjoy collecting items that have both Lugia and Ho-oh on them.
Ok, let me be honest: I'm not actually all that fond of Ho-oh. I just couldn't take him very seriously after I realized that his tail looked like a Voltorb exploded in it. (Plus he just looks so angry all the time! Although I suppose if a Voltorb exploded in my butt, I would be quite displeased as well.) I much prefer Lugia (in fact, he shares the title of being my favorite legendary Pokemon with Mewtwo) because I love his sleek and almost dragon-like design. However, Lugia and Ho-oh together make up my favorite "titular" legendary pair (e.g., Groudon and Kyogre, Dialga and Palkia, Zekrom and Reshiram) because I personally think they have the best design and complement each other very well. In short, I love their duality. As a result of this, I enjoy collecting items that have both Lugia and Ho-oh on them.