Seal of Command has a chance on a successful melee hit to deal
Judgment of the Crusader is much better than its seal. It acts as a debuff that makes the enemy vulnerable to holy damage and increases the amount it will take aion gold up to a certain amount. This is one of the only debuffs in the game that increases holy damage.
If you are soloing a hard monster then it is usually best to enter battle with Seal of the Crusader and immediately judge the enemy. With the debuff up you can then use a different seal that deals holy damage like Righteousness or Command to increase you damage substantially.
Seal and Judgment of Command: This is the hardest hitting of your seals and the absolutely best way to increase your DPS as a paladin. Seal of Command has a chance on a successful melee hit to deal extra holy damage equal to 70 percent of your weapons average damage. This means that the higher your weapons damage, the more extra damage you will deal.
Command also has a mechanic that will let it proc seven times per minute. If you have a fast weapon you will swing more times per minute and have fewer chances of it triggering a proc. (1.50 speed = 17% chance of a Command proc.)
But if you have a slow weapon you will swing fewer times and have a higher chance. (3.00 speed = 35% chance of a Command proc.) These two factors mean that the best weapon to use when using Command is the hardest hitting two handed weapon you can find.