The Dragoon is one of my all-time favorite classes. Dragoons equip exclusively Lances and their signature ability is their Jump attack. Dragoons will leap into the air, avoiding damage for one turn, and then attack for roughly x1.5 damage at minimal job levels. The multiplier goes up with job level and can become quite ridiculous very quickly, especially since it mitigates damage for a turn! Jump attacks, regardless of Lance, also inherently have the Wind element, making it especially powerful on enemies weak to wind.
While Dragoons will initially start out with very weak Thunder Spears, later dungeons will literally give you free Dragoon armor and upgraded spears, from the Heavy Lance to the Trident to the Blood Lance. All jobs are usable and equally viable, but honestly the Dragoon stands out from the rest as a particularly powerful powerhouse. I strongly recommend you have at least one on your team, just like you would have at least one White Mage.