Essentual units to use 'Alt-Click' with

[vartan]

heavy cavalry.

Not if you're playing the AI or humans that don't use secondaries with their cav.

@Conan It isn't as simple as the secondary weapon being better than the primary. AFAIK there are bonuses for spears against cavalry, but no such bonuses when using swords or something else. So the question isn't complicated enough. You should ask: What type of unit am I using, and what type of unit am I up against? Then you can figure out by calculation which weapon is appropriate in that setting.