Definitely Monaco, but mostly because for a long time it was the only event for which I had TV coverage whatsoever.
I think first time I was able to watch Le Mans 24h was in 2005 when I got Eurosport. Didn't know the teams nor the drivers (except JJ Lehto and Allan McNish). All those different car classes were an odd world for an F1 fan. After a few of hours the gaps were +5 laps, so how can there be any battles and overtakes anymore...boooring. Yes, I was a newbie when it came to endurance racing. But after I stopped subscribing Eurosport in 2010, I have only watched the race from crappy streams. Couldn't really stay up for 24h anyway.
For Indy 500 I have never had a proper coverage, only to rely some random streams. The first race I watched was maybe in the late 2000's, but can't even imagine what quality of those streams were, not HD for sure. Again, the same problem as with Le Mans: You cannot get attached to the series when you don't know any of the drivers nor the teams. They are just random-generated names. It's really difficult to follow the race, when you don't know who's supposed to be quick. The rules of Indycar are pretty weird compared to F1 and the pit strategies feel random. I've tried to watch every event for the past 10 years, but to this day, I still don't feel I really care about Indy 500.
But Monaco Grand Prix is special. I have watched it since I was a little kid. I raced in Monaco as Mika Häkkinen in F-1 World Grand Prix for N64. I know everything about the track and everything about F1, so I feel completely comfortable and hyped every time the cars leave the pit during FP1. I've even visited Monaco, so the place has a personal significance for me. It's a tradition. It's a highlight of the season.
You might hypothesize that if it had been the other way around, i.e., having watched Indy 500 and Le Mans since the 90s, but lacking official TV coverage for F1, then it might be a different story. But as we know, early childhood experiences explain a lot what you like as an adult.
Edited by Ruusperi, 30 May 2023 - 14:27.