What is the best class for killstreaks in Cod Mw2?

Hey guys, i cant seem to get high killstreaks in cod mw2. I have my killstreak things as predator, harrier, emergancy airdrop. I got the airdrop about twice...and my highest killstreak was like 20 something because i was VERY lucky, and now, i can only get 5 kill streaks on a good day, Please let me know a good class, and any tips on getting my killstreak to atleast 8 on a bad day, thanks alot guys!