NWA without a doubt.
I agree it's a generational thing. Younger people probably don't understand the impact NWA had.
For the younger crew, imagine if a rap group came out tomorrow that OVERNIGHT made 2Pac, Biggie, 50 Cent, Eminem, etc all look like sunday school teachers. how huge would that be? How much FURTHER would that act have to take things?
That's what NWA did. Plus, the whole of the NWA parts is greater then Biggie. A solid case can be made for either Dre or Cube going up against Biggie just by themselves. Add in Eazy E, Yella, and MC Ren, and The DOC (God rest his soul) and this is NO contest.
Plus, NWA was just hysterical too. I defy anyone not to laugh their arses off to the classic "Automobile" on the niggaz4life album. It makes a good Mothers Day gift too!