The choice also depends on the opponent. For example, against Necropolis, many dark spells are not very effective. But the advantage of dark magic is that it has a cool perk – the Fallen Knight, which increases spellpower by 5 when casting dark spells, although it reduces defense by 1. However, if you have leadership, this won't be noticeable. In this case, by adding a couple more artifacts that boost spellcasting, you can cast high-level spells quite effectively. On the other hand, light magic is also quite effective against knights. Increasing the speed of a large group of units with low initiative is a good strategy. Mass Divine Power at the expert level is also devastating (archers, royal griffins, knights Isabelle, and seraphs deal tremendous damage). Against Necropolis, as an option, you can consider the Eternal Light perk.