Well, on a "good/evil" scale <not saying that any of the dragons are particularly "good"> I would say that it breaks down a bit like this:
Regulos: <Of course> He wants everything dead....end of story.
Maelforge: Again, mass destruction of everything....only to start it all over again in a never ending cycle of chaos and pain.
Laethys: Greed incarnate and wanting to own EVERYTHING, not caring the pain and misery it causes.
Greenscale: He wants everything to revert to primeval "predator/prey" where only the strong survive. Kind of like Tavril with PMS and in a REALLY bad mood. Hardly good, but not really particularly "evil" either, if you step back and look at it.
Akylios: Madness is never really "evil", per se, though it's actions can be. In his madness, he wishes everyone else could be mad like him...possibly so everyone can understand what he does....and he won't be alone anymore.
and lastly, Crucia: Arguably the least "evil" of them, as far as the civilization of Telara is concerned. She seems to not want chaos and destruction, but instead order and peace....taken to the extreme. With, of course, Herself as God-Queen of Telara. Her methods, however, leave much to be desired.