Likely a cliched answer, but it's Lugia for me. Sure, it's the "overrated" choice here, but Lugia is one of those long childhood favorites that you grew up always admiring. My taste in Pokémon, and all things really, has always been for a more simplistic and modern style design which is what Lugia has always had in my opinion.
For me, Ho-oh's design (and it's typing) has always put me off about it, and it's one of the main reasons I was always more drawn to getting Silver and later SoulSilver than I was to Gold / HeartGold.
Plus you gotta admit, Shadow Lugia from 'Gale of Darkness' was just plain awesome!