I don't mind Beautiful Tomorrow, but it's always struck me as a bit simplistic and treacly. I much prefer Best Time, both in terms of its music and its meaning.
Ironically, though, the meaning of Best Time is subtly subversive in that it's actually antithetical to the idea of both Tomorrowland and, in a broader sense, the essence of "Disney" itself: the song asks the listener not to become preoccupied in fond memories of the past or hopeful daydreams of the future, but rather to enjoy the here and now. In urging the listener to grasp the present -- whether it be "a time of joy or strife" -- I always found a touch of the profound in the song. It evoked a bit of the idea of Thornton Wilder's "Our Town," and its ending -- where the audience realizes that very few people value life as it's lived, minute by minute, in their preoccupation with pining for the past or yearning for the unknown future. Although the theme of Best Time touched on inherently melancholy issues of mortality, I always left the CoP feeling happy and resolved to enjoy my vacation and my life -- because we each only have a single life to live: our own, and no one else's. For that reason, I always appreciated the CoP -- not just for its AAs or effects, but for transcending its own nature as "just" another theme park attraction.
In contrast, Beautiful Tomorrow is a catchy little ditty that adequately fits the theme of the attraction -- but without imparting any deeper meaning to any of the acts or eras lived through by the show's AA figures. It's fine for what it is, but disappointingly shallow in comparison to its predecessor.