Dragons vs. Balrogs?

[Kuruharan]

But think of Smaug. One arrow and he was down. Not much of a fight, aye?

again...

We do not know what would have happened if Legolas had been able to get ahold of himself and shoot the Balrog. Smaug was all distracted and enjoying himself town-baiting when Bard shot him. If Smaug had been paying attention to Bard, he would have ended up one crispy critter, rather than king of Dale. Legolas had a similar opportunity to shoot the Balrog when he was paying attention to Gandalf. Who knows? The Balrog might have had a convienent hole in its armor (or hide) and that would have solved the problem.

Anyway, recap...
Balrogs-maiar
Dragons-maiar
Similar spirits, different tools, would have depended on the circumstances, who was fighting, no clear cut advantage to the Balrogs.

Dragons...are imprisoned in one form.

To quote Thingol...

Also Tolkien specifically stated that the Balrogs became bound to their bodies permanently. This probably occurred after the Battle of Powers.

Balrogs were bound to their forms as well.
And as we discussed (at length) earlier Melkor also put his power into his Balrogs as well as the Dragons.