Light arty is better than heavy if you are going to need to move around a lot, both on the map and in simulated battles. Its range is better than mounted arty, so is particularly useful with infantry, whether on attack or defence. Strategically it gets used for sieging fortresses. Used tactically in a simulated, it gives you the ability to shoot at the longest range. Best used in defence, sited on hill tops behind the fighting line, it can also be useful in slow methodical attacks.
Cuirassiers benefit from armour, reducing losses.
Best viewed as panzers in combat, capable of stopping enemy advances or spearheading your own. Usually the strongest units on the battlefield. Much light cavalry has a firepower rating and so scores extra in mathematicals. These troops make good skirmishers in a simulated, able to move fast to take positions, fire upon enemy troops, and screen other activity. Major advantage is the multiplier when fighting infantry in a simulated.