At the awesome "Experience Hendrix" tour last year, EJ blew the audience away. He and KWS were the highlights. KWS is fantastic live, so much better than studio albums. But that goes for pretty much all blues guitarists. Buddy Guy was entertaining and humorous, but his playing was very sloppy and erratic, not in the same realm as EJ or KWS. BG came across as the legendary old guy who can still kinda play. Zakk Wylde was ridiculous in both good and bad ways.
That said, live blues is all about passion and feeling. On a given night, I could see Buddy Guy being "on", really digging in and wowing the crowd while a guy like EJ just wasn't feeling it on the same night. Not to mention EJ would likely let BG "win" simply out of respect. Imo, generally speaking, EJ is a far superior guitar player, but Buddy Guy is a better live "entertainer." If I want to be dazzled by a guitar player I'll go see EJ. If I want to kick back, have a few brews and be entertained with friends I'll take 'em to a Buddy Guy show.