I'm in favor of several names for them, and I'm thinking of this for my campaign:
Dragonborn - Their formal name, and how most educated people refer to them. 
Dragon-men - Commoners tend to have a simplistic view of things and some call them this...but it's not considered a disparaging term in most contexts.  
Drakken - An alternate name, used perhaps by a culture from a different continent than the main campaign.  
Coldbloods  - This could be a disparaging nickname, used by those who distrust them. 
Dragon-men actually is growing on me as the most common term.  It's kind of dumb, but at the same time I can easily imagine humans, dwarves, etc calling them that, as it is certainly a good description, and no more intrinsically disparaging than "halfling".