I... honestly cannot decide which one I like more! I've always been big on Lugia, but lately Ho-oh has caught my attention more due to its unique-sounding battle theme, its greater lore involvement, its warmer color palette, and its association with the sky rather than the sea. Lugia, however, also has an amazing battle theme - possibly the most intimidating in all the franchise - a better cry than Ho-oh, and an interesting design history.
Ultimately, I choose Ho-oh solely on the basis of its typing, because I prefer Fire-types over Psychic-types. That, however, doesn't mean I like Lugia less. It's about equal for me.