Dragons have an organic aesthetic- like literal flesh-and-blood creatures, only made of metal and plasma. Their appearance varies just as wildly as the Shard Patriarchs do, with some looking more humanoid, some looking more animalistic, and all having some kind of reptilian/draconic features to them. Think of this:
...and you’re in the right ballpark.
A Dragon is better than a normal tank because of three things- power, speed, and flexibility. Power, because their weapons are strong, their bodies durable. Speed, because despite being anywhere from 20 to 90 meters, they move with such speed, grace, and reflex as to be impossible by armor or artillery of comparable size, and flexibility because they can be used in any theater of combat, and, being living creatures, can learn from their mistakes and victories along with their Pilot.
Technology is to the point where personal plasma weaponry is relatively commonplace, and the Dragons themselves can do weird, pseudo-magical bullshit like ferrokinesis or Roboteching their lasers, depending on the particular frame.