Limit 3 isn't fair. Need at least one per decade! These may not be the "best," but were definitely the most memorable.
80s. Iron Maiden - Somewhere in Time. East Rutherford NJ. Imagine having to explain to your mom when she picks you and your fiends up afterwards why the cops and fire dept are there extinguishing burning cars.
90s. Quicksand, Surgery, Therapy? at the Academy NYC. From asking the one drug dealer why he thought we'd buy from him instead of the 10 others we just turned down and having him say in perfect Queen's English, "well I do have a better selection, prices, and quality than my compatriots here." to people literally diving off theater box seats into the pit.
00s. The Starting Line, Early November. Starland Ballroom? Getting older. Hanging in the back with the adults when during a conversation one of them asks, "Which ones are yours by the way?" I didn't understand the question was related to kids, but the girlfriend immediately replies "Whichever ones we can force into the van the easiest." After that, we had an amazing amount of elbow room.
10s. Hard to decide between Slowdive's reunion and Snapcase's here. Both were absolute bucket list shows of bands I desperately wanted to see back in the 90s but never could.
20s. Dreamwell, Stay Inside, For Your Health. St Vitus NYC. By now I'm the grandpa with the granny reading glasses falling of my nose cos i'm too afraid of losing them and not being able to navigate public transit home without them.
To all the other folks getting up there in age, I implore you to keep going to see shows, and not just of the same bands you've been listening to your entire life. It's not that difficult to find new music if you've an open mind and a little time to explore.