Hi Mary,
I don't know how long ago it was that you saw Gregg but here's a link to the short review I wrote after his last appearance in London in July 2011. As you'll see I was not disappointed. I saw BB around the same time and I know who I'd go to see again if I had the chance. 17 songs from Gregg versus a few anecdotes, a little playing from BB and a lot of playing from his band, means it's a no contest for me. I did enjoy BB but I felt once was enough. I have read similar comments from others who've seen BB more recently.
I am a self confessed Allman Bros nut so I am somewhat biased. 
My thoughts would be to see Gregg and remember BB as he was. Please let us know your decision and how the show goes.
Phil
Ars Longa, Vita Brevis
“The guy who has helped the blues industry the most is Joe Bonamassa and I would say he is more rock than some rock stuff, so to me blues is whatever you want it to be!”
Simon McBride in my interview with him in Blues Matters! Issue #56