It's fair to say that as they're all such polarised extremes it's hard to choose. I did say on another thread that I'd jump on board with Deirdre to Planet, but...
For Earth:
Morgan - isn't this how our planet's going anyway? Capitalism means that some people are going to be with, and many people are going to be without, but more people are with than if you tried to reduce everyone to the same level of poverty. Then once the some have their money, they are empowered to do whatever they want with it. The monopoly does seek to remove competition, but it would know how to balance itself to remain profitable, by not destroying the market and the economy.
Deirdre - Being green, liberal and democratic is appealing, but would probably cause us to regress centuries by dismantling the industry and economy with half-baked ideas. A lot would depend on if she looked for workable green alternatives (which may eventually come about, they don't exist yet) or if she just rejected industry out of hand. At least the liberal democracy would have the freedom to think up of these things, and engage in science.
Zacharov - The promotion of science and free flow of information - fantastic! I have no problem with current ethical standards, but this characterisation would probably push it over the limit of tolerance, and studying science at any cost is a bit unpalatable, and potentially anarchic. People could twist whatever they wanted in the name of science.
Santiago - On the interpretation that they arm themselves to defend themselves, and not to attack others. But all that power would be rather tempting for a leader to use... and too much money would get spent on maintaining the military, not the economy, and you get a banana republic.
Lal - Ideologically alright, but realistically layers and layers of leftie bureaucracy, I'd imagine he's big on democracy but actually quite undemocratic himself if he didn't agree with something. And they'd be self serving, they would make sure they looked after themselves before anyone else. At least Morgan wouldn't lie about it, and he'd only be thinking about the money anyway. Think being governed by the United Nations, and think whether you'd ever get anything done. I'm probably being a bit harsh, putting this below the banana republic.
Yang - He would make Communism work, to his blueprint, but his blueprint is not a design for life - it would be an inefficient, harsh, brutal world. Or, if that's what you think the world is now, then an ever harsher, cripplingly inefficient, brutal world.
Miriam - Religious fanaticism to that extent is just scary, and counter productive to progress by the lack of freedom of thought and ideas. Yang's rule would suppress free thought too, but through force, not brainwashing. And he'd secretly understand the need for someone to come up with a good idea, though that person may not get any reward for coming up with it. The fanatic would believe in their infallibility.
I'd go with a Morgan-Deirdre combo, which probably is wrong to do here because they're such opposites and what I'd really like is something in the middle.