The 41-year-old Spaniard has battled many world champions throughout his lengthy F1 career but believes seven-time world champion Schumacher was the toughest of the lot.
Alonso brought an end to Schumacher’s reign of F1 domination when he beat the Ferrari driver to back-to-back titles while driving for Renault in 2005 and 2006.
“It is difficult to pick one because they were all great rivals and very talented drivers as well,” Alonso told Bang & Olufsen.
“When I came to this sport, Michael Schumacher was dominating the races and everything, probably that fight with him would still be the one I would choose.
“Fighting against Michael was very special, so I would say that.”
Asked to pick the best moments from his illustrious career, Alonso replied: “All the memories from different teams are very linked with the results I got in that moment.
“For Ferrari, I will pick the first race I won. Aston Martin, obviously I will pick [Bahrain] where we got the podium, and from Renault I will pick the championship.
“The biggest one was the first championship, always the first championship. The second was obviously emotional, but the first one was like a dream come true, and a life goal.”
Alonso has enjoyed a dream start to life at Aston Martin, who have proven to be Red Bull’s closest challengers in 2023 following a sensational winter turnaround.
Alonso has already claimed three podium finishes from the first three races of the season and is dreaming of ending his decade-long wait for a 33rd career victory, as well as winning an elusive third world title before he retires.
“I always believe it’s possible, that’s why I keep racing,” he said. “The challenge is big, you know that you need to overcome some difficulties and some top teams who are at the top of the sport.
“But I race every day and I train every day thinking that the third title is possible.”