Hahaha, I mean... my comic is literally one where a guy makes himself King and the other characters are trying to usurp him, so... we kind of have some literal examples here...
Worst, as we legitimately see in canon because he's King and he's the villain having made himself King.... Urien Ellis:
On the surface, Urien seems like a good guy for the job. He's a good public speaker, he's handsome and fashionable, he has amazing hair, and he's fairly intelligent.
...Problem is he's also extremely vain, opportunistic to the point where he doesn't think ahead about the consequences, unwilling to take responsibility for bad things, instead always blaming others, gaslighting and changing the subject. He loves the part of being in charge where he gets to be the centre of attention and have everyone fawn over how powerful and important he is...and then would rather have somebody else do the thankless hard work. He's also very emotionally driven and will make bad choices based on fear or jealousy. Basement tier president, even if he does rock the look.
Sitting firmly in the mid-tier, but worth mentioning because they're the one actually campaigning to replace him... we have his younger sibling, Jules Ellis:
Jules is frankly, not really suited to being a monarch or a president, and it's kind of a testament to just how bad Urien is at his job that anyone would even consider it. The area where Jules would be excellent at the job is that they are a cautious and practical planner who always thinks ahead, and they genuinely care about looking after people's welfare.
The...er...problem is that Jules isn't much of a diplomat or politician; they're typically autistic in socialising, with a tendency to be very blunt or to come off tonally inappropriate for the situation, and they find people tiring. About the closest they can get to an appropriate persona for politics is "acting like a supervillain". Again... Mid-tier.
So who's the actual best president in Errant?
I've actually always thought it would weirdly be Rekki Lune. Of course, she's out of the running to be a monarch, being not an Excalibur candidate, but...
Rekki always leads by example. She'd never get you to do something she didn't think you could do, and she'd never waste your time or your life for no reason. If she can fight the monster herself, she'll do it. Yes, she does have a bit of a tendency to try to take on all the problems herself all the time, but hey, she's at least a very responsible person who owns up to her mistakes! She's a strong leader, and when she gives an order, people do tend to follow it. She's a bit of a fashion disaster, but she has a lot of presence. She's not incredibly crafty, but she's smart and humble enough to listen to people smarter than she is, and I think this down-to-earth quality would make it a lot easier for her to relate to ordinary working class types than people like Sarin or Jules with their high ideals and convoluted plans.
So I'm going to vote Ketchup-Head for Prime Minster of Britannia here. Elrekia Lune is the winner!