The esper and herald classes do not have much in the way of mechanical overlap, nor do they overlap in their preferred ability scores. Heralds need Strength for weapons and Charisma to drive their supernatural features while espers need Intelligence. This means that in most cases, you’ll probably want to emphasize Strength and Intelligence with Charisma as a tertiary consideration. Which of the two primary scores gets more attention should correspond to which class gets more levels - Strength for herald and Intelligence for esper. Flavor-wise, this is an unorthodox mix. Generally-speaking, heralds tend to be very straightforward individuals and espers tend to be more subtle, and heralds also have a strong ideological/ ethic component as a fundamental part of their class identity, whereas espers do not. Player will want to think about what this mix looks and feels like for their specific PC. More levels of esper gives you a powerful mentalist with a sideline of combat skills and strong devotion to a guiding set of principles. More levels of herald gives you a fairly typical-seeming ideological champion with some mental abilities on the side. An even mix of the two is a character with a lot of different supernatural abilities from multiple sources and some credible combat skills as well. [[Synergy Feats for Multiclassers#Esper w/ Herald|Esper-Herald chains and ideas]]