At the time Isles had to choose between a #1C with crazy pre-draft hype, stellar WJC and potential instant face of the franchise talent vs. a lesser known but hugely talented D man who also was stellar at the WJC and coming out of a European league. JT was more marketable and was the right pick for the Isles. I don't think in a redraft with the Isles picking 1st overall, Hedman ever goes before JT. Just business wise it's a terrible decision.
Hockey players wise. Both have been excellent players and like some have already stated, franchise level d-men typically age better than franchise level centers. Also, the supporting cast JT had in NY was absolutely trash and he essentially had to build up that franchise. Where as Hedman seemingly walked onto a consistent playoff team who were cup contenders not too long prior. Plus he had guys like MSL, Stamkos, Lecavalier, Tanguay, Ohlund, Gagne, Malone, etc. to rely on and learn from while he was being groomed. His development was much steadier and slower compared to JT who was tossed into the fire and expected to not only survive but Thrive. Which I think he did a great job of doing.
At the end of their careers, I suspect Hedman will have a cup or two and norris and conn smyth trophies to show for plus a HOF resume. JT I think will also be a HOF player but much less hardware.