For me it's the 80s - variety of playing styles and court surfaces, graphite racquets taking over, power tennis but still room for artistry, athletes starting to place more emphasis on fitness, and the various player personalities. I suppose most of that could be the 90s too, but I found those days had too many big serve fests. 70s - loved the artistry and different playing styles, but big power wasn't there yet. 60s - can't say I know a whole lot, but it seemed like a lot of S&V only, amazing stuff though. 50s and before - I have no idea, so can't really comment.