On my hunter this is my kill priority
1. Rogue - If you don't kill him before he gets into stealth you are probably going to die.
2. Druid - Druid's should be at the top of everyone's list because their healing is devastating because their hots can heal everyone so fast.
3. Warrior - They can rip us hunters up with their hamstring and their damage they can do when you are slowed and their deadly MS.
4. Hunter - We can burn down on someone not expecting us really really fast not to mention that deadly MS we throw out as well to minimize the healing makes us a big threat.
5. Warlock - Their dots can tear up anyone in a 30 yard radius, including the healers healing you, as well as their fear can wreak havoc in a fight.
6. Mage - Just cause they are squishy and when you kill them thats one less dps to have pounding on you.
7. Death Knight - DnD can cause alot of damage in a group of your allies as well as the diseases they can stack on you and your healers.
8. Paladin - Paladin's are a nuisence to kill first cause you know that they will buble right at 10-30% and then you will just have to switch to another target anyway.
9. Priest - Really squishy and you can rip right through them no matter the spec.
10. Shaman - Also really squishy the only spec you have to watch out is being "out-bursted" by an Eleshaman other wise Resto and Enh are easy to rip through.