I think this is definitely Jagr. It was clear he was the best player in the regular season. Pronger won the Hart, but it was by 1 point and Jagr missed 1/4 of the season. He still won the Pearson, the Art Ross, and dominated the field in per game scoring. This despite no one on his team having an exceptional offensive year. I think you’d could argue Jagr was playing his best hockey that season, even if the year before was his best full season. He also had the better track record coming into the year than Pronger.
Meanwhile, Hasek, his strongest competition, missed time and wasn’t as good as his peak that year, and while he won a Vezina the next, was never peak Hasek again, suggesting this year was clearly Jagr passing ahead. Sakic had a really good year, despite missing 1/4 of the year himself and was probably the second best forward per game, but he had a poor playoffs, while Jagr had a good one. Forsberg had a poor year by his standard and missed significant time. Lidstrom was Lidstrom, but I don’t think he was as good as peak Jagr.