While Lucario may have a larger physical movepool. It also has access to useful special moves, making it a very versatile Pokémon. It's defense, however is nothing short of useless, especially with Close Combat.
Lucario has higher special attack than attack, but barely, and a Mega Lucario has a slightly higher attack stat. But it would be a shame to just ignore the special attack. If you have to choose an attack boosting stat, go with Lonely. But on a Mega Lucario with Adaptability, you should have a speed boosting nature, like Hasty or Naive.