Cool...a thread about dragons.
ALL? Please. Either your DM is: 1.) running them wrong
2.) running you wrong
Be careful, my brother. While dragons should be respected and feared, heroes ARE rather tenacious and very often will triumph over even the fiercest foes. As hard as it may be to believe it, dragons have actually died in my campaigns, although they have always done quite a bit of damage before being sent into the loving claws of Tiamat.
We must strive to make sure that DMs are well prepared enough to make sure that any encounter his players have with dragons is the stuff of legend....
As far as deadly dragons go, I've always had a special place in my heart for blacks and greens. Black dragons, although not the most intelligent, have an acid breath weapon, which is just cool. Acid is not to be underestimated. I have always ruled that the bodies of black dragons are suffused with acid, so that their blood and flesh are toxic as well. Lots of fun to be had there.
Green dragons seem to have a lot of style. They're beautiful and sleek. My own high level character, an elven fighter/wizard named Kayen Telva (after a pregenerated character in the original Slave Lord series), fought with a green dragon for several decades before finally defeating her.