I think it's a tough question. There may not be a single source of Iodine that is "best" for everyone.
But lots of folks will have their own personal favorite source, and if confronted by a second person who has a different personal preferred source, it can become an opportunity for unproductive exchanges. I know a lot of really old people who have never eaten kelp nor taken Lugol's or Iodoral, etc. Iodine is deemed essential, but it certainly is possible to live a very long time without supplementing it.