NWA, or Nigga With Attitude, is one of the most influential group in Hip Hop, not because entirely of their persona, but the undiluted streetness that they protrude in their lyrics and songs. Their careers took on a greater influence on hip hop separately than they had ever influenced it together.
Adrenaline! - The Roots. It's really hard to pick just one or two The Roots songs. Especially since (tragically) they're best known as Jimmy Fallon's backing band, so you, as a long time fan, want to pick THEIR BEST SONG EVER. All their songs are their best song ever.