That's hard to narrow it down to just one, or even a few.

Festival style/multiple artists:
1) Forgotten the name of it but it was an all day country show at Atlanta Motor Speedway in 1996 lineup was Kenny Chesney, Tracy Byrd, Pam Tillis, Patty Loveless, Charlie Daniels, Hank Jr., Alan Jackson and Alabama.

2) 2001 George Strait tour at Turner Field. Asleep at the Wheel, Brad Paisley, Sara Evans, Leann Womack, Lonestar, Alan Jackson and King George.

Single artist shows:
1) Vince Gill at the Omni, Atlanta, 1997. The last concert at the venue before it was torn down to build Philips Arena. He played until well after midnight, just song after song after song.

2) George Strait 2010, Philips Arena, had Leann Womack and Reba open for him. Of the 8 times I have seen him, this was the best. One of my top bucket list items is to see him do a show at Frontier Days in Cheyenne.

Honestly, looking back on it now, the Grand Ole Opry last spring was really a great show. Been to the Opry many times, but this was the first show after they had announced the 2015 Hall of Fame inductees, and those still around where there and performed, so we got to see the Oak Ridge Boys and the Browns (their first performance together in 10 years or so) and this was just a few months before cancer got Jim Ed Brown. Also got to see Sturgill Simpson live for the first time, which was really exciting.