Against, say, the Seleukids, I find very hard campaign to be an exercise in some sort of madness. That's no shot against EB despite how it might sound. But having to fight off three or four full sieges/stacks each turn from one faction alone can become truly exhausting. Especially if I'm playing Hayasdan...

When I'm playing the Romans, however, I kindof enjoy the "barbarians at the gates thing" that comes with the very hard campaign level.

In any case, I'd never touch anything above medium battle. No sense in giving the AI units unrealistic bonuses. I prefer that my elites can beat a skirmisher, and that might go away on very hard. :p