Best Box Legendaries?

Surely Mewtwo isn't a box legendary because it doesn't appear on the box of a Pokémon game. Kanto doesn't have box legendaries, though arguably the Kanto starters might as well have been legendary in gen 1 due to the lack of a breeding mechanic. They were ironically less accessible than the actual legendaries.

Is this question in terms of which box legendary was the best competitively, best design, best theming... or all of the above?

I am not the biggest gen 4 fan, but I like the box legendaries. Reshiram and Zekrom are pretty good, too.

Among my many criticisms of gen 3, I never liked Groudon or Kyogre. They look like creatures from a different franchise to me.

Xerneas, Yveltal, whatever the two dogs in SwSh are called in English... they all look fine. Whatever. No strong feelings.

Koraidon and Miraidon being bikes was stupid. I don't care how they try to justify it. They look stupid. I actually prefer Miraidon slightly because at least it having wheels makes sense for a robotic creature and they are used in-game. Koraidon's vestigial throat-sac wheel thing ruins what would otherwise be an okay design. It looks as though it would do nothing but hinder the creature's speed, which is the exact opposite of what you want from a mount.

I think Ho-oh and Lugia still stand out to me after all these years. I really like Lugia, but I think they are really striking with the gold and silver colours of the boxes, and they came at a time when legendaries still felt special and mysterious, following on from a time when all we had was Mew, Mewtwo and the birds. Legendaries in later games feel like an obligation. "Oh, another batch of those guys to catch." I rarely even bother to go out of my way to catch them if the story doesn't force me to.

Both were impactful in the anime, one being a mysterious hint to future games in the very first episode, the other being the focus of the second movie and leader of the previous game's legendary trio.

Perhaps it is childhood nostalgia to a degree, but Ho-oh and Lugia's clean and simple, yet imposing designs still fill me with wonder to this day.