Questing in the starting zone
When leveling it really doesn't matter because all of the are great specs for DKs are great. Even though that they are good you can get the best spec for leveling. I prefer frost or blood depending on your personal preference. it doesnt really matter how u spec them because of the new Cata talent trees i will go in to more detail in my Blood and Frost pages that will be coming out soon.
The main gear that you will try to get for DK dps is to stack strength, crit, master, hit and other melee dps stats. If you are a blood tank you will get also strength but you will want also parry, dodge and stamina.