[Wrana]

Considering heat/cold I think that it should mainly depend on your nation AND your opposition. While cold/heat-loving nations are completely clear, we can see also that if you have good access to water spells and no such to fire, you should probably take at least 1 cold and vice versa. At the same time, if you see that your most dangerous opponents would be, for example, Abyssia - or cold-blooded C'tis, you should think about Cold, and if it's LA Atlantis, think about Heat. Of course, it's not always clear which opponents are most dangerous, but at least that's something to work with...