Technically, my favorite years on the Aperture timeline are between 1951 (when Caroline got hired) and 1967 (when shit started to hit the fan) -- but the reason I love the late 50s and mid-60s is because that's when Caroline really comes into her own. In those years, she goes from naïve but enthusiastic assistant to undisputed Head Bitch In Charge. She sheds her shyness and discovers the no-nonsense confidence that lets her be Cave's right-hand woman. Early 50s Caroline is cute and sweet, but her potential remains mostly untapped -- 60s Caroline runs the place and knows it. She knows her job, she does it well, and she isn't afraid to take care of anyone who gets in her way. And of course she's a tiger in the sack.
Beyond Caroline, though, I think of the 60s as the time when Aperture really flourished. They came to quick success in the late 40s, and did well in the 50s, but the 60s was their Golden Age -- Cave had the big dreams, and Caroline made them happen. They were rich, they were famous, and they could take on anything the world threw at them. They were unstoppable.
Until the Poopy Joe debacle, and the missing astronaut hearings. Then their history of mysterious disappearances was discovered, their reputation tanked, their products got more and more controversial, and money stopped rolling in. Even years before the moon rock incident, the 70s were a dark time at Aperture -- but they had the memory of past success to keep them going, and keep going they did. These things were only temporary setbacks. They'd be on top of the world again soon.