I think Eminem by far.
If Kendrick ever wanted to start a beef, and if Eminem had legitimate reasons to respond, as he did when MGK brought Em's daughter into it, Eminem could find a way to easily destroy him in a hit song that would probably be the biggest chart topping diss track of all times.
Kendrick would have to just silently move on...
I don't ever see that happening though, because the fame Kendrick already has.
Small artists only go after Eminem in hopes that he'll make a career for them by just mentioning them. In one song, I can't recall, Eminem even references such by stating that he named them just to give them a career to destroy it and then went on to completely obliterate them so they couldn't have a career from the mention. It was such a good attack, I don't recall who it was for—possibly MGK again?
Dr. Dre is still good too. He has a lower voice than most rappers, which gives him a unique appeal.
I will have to listen to more Kendrick Lamar to see if I can rank him up with Eminem. So many people are mentioning that he's the best, but I have honestly only listened to his Drake diss, Not Like Us.
That said, Eminem's list:
Eminem - Till I Collapse said:
I got a list, here's the
order of my list that it's in
It goes Reggie, Jay-Z, 2Pac and Biggie
Andre from OutKast, Jada,
Kurupt, Nas, and then me
From his list, 2Pac and Biggie were big when I was a kid. Still throw those two on during workouts too.