Alrighty. I've spent some more time going over the options, and I've also read up a bit on some of the game mechanics that I'm not familiar with.
One of the things that really stood out was that Courthouses grant espionage benefits. So I took a look at all the civs that offer Unique Buildings that are modified courthouses:
Aztecs Montezuma = Aggressive/Spiritual, Mysticism & Hunting, Jaguar (sword), Altar (court)
HRE Charlemagne = Imperial/Protect, Myst & Hunt, Landsknecht (pike), rathaus
Sumer Gilgamesh = Creat/Protect, Wheel & Agric, Vulture (axeman), ziggurat
The Lansknecht is a really powerful unit - 6

, +100% against both mounted AND melee

However, the rathaus costs the same to build as a regular courthouse - 120

, whereas the ziggurat only costs 90

Sadly, the protective trait means that nobody would really want to mess with us anyway, so we'd have to go looking for trouble to take advantage of them
Of this list, I'd go with Sumeria. Creative is a huge benefit in the early game, and their axemen are beefier against melee units: attacking at 8

instead of 7.5. In this case, we're safer later in the game because of the protective. But I'm still not convinced that protective is useful in MP.
In addition, none of the civs that have jazzy courthouses start with Mining, which I think is the most important starting tech. The sooner we can get Bronze Working, the sooner we can start whipping!
This led me to consider the civs that start with Mining. Boy, there were a lot of them!
13, in fact - with a total of 21 leaders
So I narrowed the field by selecting Financial, Expansive, Spiritual, Charismatic, and Imperialistic, and Organized - the top contenders from our earlier poll. Results:
Hannibal Carthage: Financial/Charismatic, Fishing & Mining
Asoka India: Organized/Spiritual, Mining & Mysticism
Mansa Musa Mali: Financial/Spiritual, Mining & Wheel
Pacal II Mayan: Expansive /Financial, Mining & Mysticism
Carthage has the jazzy harbor, and great UU.
Asoka has the fast worker and jazzy jail
Mansa has the skirmisher and jazzy forge (a great UB, btw)
Pacal II has the Holkan (spear) and jazzy coliseum.
I guess the problem that I have with the Protective trait is that it's only good if someone comes after us. But wouldn't we rather be the team leading the attack, rather than the team absorbing it?? So Aggressive or Charismatic would make more sense.
The one civ that I keep coming back to hasn't made any of these lists yet.
The Vikings. They are a rock solid choice: Financial and Aggressive, the UB is a lighthouse, the unit is a maceman with amphibious attack. If we don't have a watery world - we don't completely lose out on the UU's strengths like we would if we were Dutch or Portuguese.
Actually, the weakness of both
Carthage and
Vikings is the Unique Building: a harbor for Hannibal, and a lighthouse for Ragnar. But if there's no coast, we can't build the buildings, and Carthage's extra happy face gets wasted. That's a big setback. At least if we go with a Jazzy Courthouse, the building will certainly get built.
I'd really like to hear some arguments against Carthage or Vikings, and please offer up other ideas (with your line of reasoning) for leaders I haven't considered, or even one I have considered and ruled out. I feel like we're not making much progress on this - and it's the most important decision we have to make right now
