Just face it, Joao is miserable any way you look at it. He's bottom tier in any comparison so there's no need to stand up for that leader. It's like defending Stalin or Mao.
That said, there's no "best" anything at anything other than on paper. Theory is one thing but the maps usually play out in a way that you can't plan ahead in the sense that you could pick a leader just for one purpose and play a game without any consideration to your surroundings.
You could say that leaders like JC lend themselves to warfare which he obviously does, but that is more because of his Praetorian rather than the traits. Sure, Imp and Org do synergize well with the kind of conquest but any leader would be a good early warmonger with Praetorians.
You can look at Gandhi as someone who's ideal for culture wins and he is but if you take a good look at him, he's actually a very adept warmonger in human hands. Spiritual is good for warring, Phi makes for slingshots and these can be leveraged.
Examples like this are as many as there are leaders and you definitely shouldn't look for "the best" but if you're adamant about it, play JC, Darius, HC; They all lend themselves to everything and are good at it to boot. Still, it is best to play Random and find out what you prefer.
HC and Darius are fun for a few times but at least I found my fancies elsewhere after having played with every leader for n times. I've come to like leaders like Charlemagne and Napoleon; Mehmed remains a strong contender and I won't say no to a vast majority of leaders actually - except for the very bottom tier. Just find your own way and your own "best" leader.