Horizons, no contest. Look, I get the nostalgic connection to Walt. But when an attraction is better, it's better. And Horizons is just better. It was elaborate with detailed show scenes and animatronic figures, had an incredible musical score and entertaining narration, was both funny AND educational plus it was incredibly uplifting and completely embodied the philosophy of progress. The designers of the ride truly put their all into this. It's simply one of the best (if not THE best) theme park attractions ever created. As much as people like to praise attractions like Harry Potter for trying new things with the ride system, I just don't think ANY new rides in the world have managed to top Horizons. From Disney, Universal or any other company. Horizons with the support of the other original roster of Future World rides were all unbeatable juggernauts of objective quality and entertainment. I think it was the best attraction up to that point and has yet to be topped. WDW and Tokyo's Splash Mountain being the only ride that has come close IMO (and if you count "upgraded clones", Paris' version of Pirates). But I still don't feel that any of them quite reach Horizons levels.
Replacing it with a glorified space spinner is among the worst travesties the company has ever done to the parks (with the exception of causing guest injury and death). I'm not saying Horizons didn't need some moderate updates to keep it looking futuristic, but some moderate updating IMO is ALL it needed to remain relevant. Either way, it's replacement is an insult to EPCOT and the Disney legacy.
Lets put it this way. Horizons and the 1994 renovation of Spaceship Earth are the only rides that have managed to affect me in such a way to actually send chills down my spine and brought me virtually to tears due to their power and emotion (helped along by the incredibly powerful and beautiful musical scores they contained along with the uplifting narrations). I was a very young child at that time, but even watching Martin's videos of it all these years later as a 24 year old male adult, I still get the same emotional impact from them. It's just a shame this emotion is now mixed with a new one- regret that I will never experience it in person ever again.
