Been to the Garden and Beacon. Never saw a show at the Rocks but did bike to it and walk around and it does not take much imagination to say a dead show there would be memorable. The Garden has a lot of energy but it is far to big, the acoustic suck, and you are forced to walk through long cooridors with billions of people, not a good thing when your in a concert frame of mind. Then again to hang out in Manhattan before and after a show is pretty sweet. Beacon is a great spot but so are alot of nice theaters that size.
Been to the SPAC sometime in the late 80's to see a show. Had a great time in the lot before the show but when I got out of the bus I was in no mind set to deal with the mass of people so I watched from the fringe. One of the worse shows I saw the Dead play so my feeling are mixed on that place.
My favorite present place to see a show is the State Theater in Falls Church, Virginia. Classic old theater with plenty of room to dance by the stage and lots of comfy chairs for space and R&R up top. They also have good beers at a reasonable price, great acoustics, easy free parking, don't hassle people, and it is easy for me to get to.