I don't know about "killing it", but I've been listening to Childish Gambino almost nonstop the past week or so.
I would say L.O.X. But everyone has their own opinion on what musician or artist or singer or lyricist is the best, and when it comes to rappers, they all think they are the best I hear to all the time, just about every rapper slips in "I'm the best rapper" in at least one of their songs, or say it in every last one of their songs
You're so right about them all claiming to be the best, and LOX is deff strong and been around for a minute.