In terms of design and battles, Lugia is more superior in my opinion. Ho-Oh is pretty much a useless Pokemon when you're battling competitively due to Stealth Rock removing half of it's HP as soon as it comes into the battle. Lugia's the best Defensive Pokemon in the game. No attack can 1-Hit KO it. As for Ho-Oh, 1 Stone Edge from the right Pokemon(even if Ho-Oh is at full health) can KO it.