Diamond Mines will earn the smallest total, but will give it to you in the shortest amount of time (less than a week).
Oil Wells will earn a slightly larger total, but it will be spread out over a few weeks to a month.
Cotton Fields will typically earn the most, but it will be spread out over a couple months.
The bare minimum for any of them is around 60 Geos. The max is well over 600 Geos for each of them.