The determination of 'best' really boils down to (as the thread starter mentioned) how long you're going to be playing in a 24 hour period. But in addition, I would add, how much attention you're willing to keep reserved for your loyalty maintenance.

If you're going to be online for a long time, and willing/able to keep a near constant tab on the loyalty while keeping tabs on everything else, then the 100% tax + disaster relief is best. Sorry Darwin, if you're going to spend enough of your focus on switching from 50% to 100% at each 'tick', then you're better off with the 100%+ disaster relief plan.

If you're going to be online for a relatively short time, or not willing/able to keep a near constant tab on the loyalty while juggling everything else, then 50% tax is better.
I think this plan will become more dominant as people expand to more towns ... just thinking of the 100% + disaster relief plan with, say 7 cities, and the constant buying of food, and waiting 30 minutes if and when someone else sells theirs (and hoping that nobody else puts a higher bid than yours while you're tweaking another one of your towns). And don't forget that the amount of food needed for disaster relief increases with your population.

Overall, those who are willing to do more micromanaging, and spend more time online, will benefit more from the 100% plan ... only in their early game. As their game develops, they're more likely to switch to the 50% plan.

As for your taxing idea UniqueName, it does show it's better than the 50% plan ... from the 100% down to 0%. But the two biggest flaws in your taxing idea are:
1. the rate of population drop; you're assuming that the time it takes for your loyalty to drop by 10% is the same length of time that your population will drop 10% (the population lags behind the loyalty, and although I haven't experimented, I think that the higher your max population, the slower the % change).
2. the other half of your example; how much gold income you'd be getting while your population is going from 0% back up to 100%. To maximize the gold income, you'd have to change your tax at every 1% change in your max population (and I don't really want to calculate that). To minimize effort, you'd put the tax at 0% on the way back up, but that also means 0 income during that time.