It completely depends on what you play and what you are trying to do. I could go into rumble pit and my KD would be 5.5 or something. If you just play team slayer and lonewolves and stuff with AR start then 1.5 and up is great. But be prepared to have a lower KD if all you play is MLG. Sometimes in a Team Slayer MLG the guy that goes positive 3 is the hero.

MlG
Below 1.00- Bad
1.00 to 1.2 Average
1.2 to 1.4 good
1.4 to 1.6 manly
1.6 to 1.8 GEO

Go ahead and run your mouth over the internet cause you damn sure wouldn't do it to my face.