I think Dragonair is better then Dragonite and is not worth giving up a Dragionair for.  Here's why:

First of all, Dragonite's pokemon power is almost never used because even if you do have a Colem or Snorlax as your active then it's better to use a switch because putting Dragonite up instead would mean useing his one and one attack which isn't that good..  Here's why his attack isn't that good:

Everyone says that it can do 80 damage so it's a good attack but it's just as likely that it does that you could two heads resulting in 80 then two tails resulting in 0 damage (this goes for all x attacks).