Hello RC Pilot,
That's a good question. From everything I've read and from everyone I've spoken to both treatments do the job. As I've only done the soaking in a steel tub in Jachymov, I really can't make a comparison (although I hope to vist the Montana mines in the near future).
My first time at Jachymov I befriended a couple from Hamburg who had gone to the Gasteiner Heilstollen caves in Austria the year before (I think that's the one where you ride around in a train underground). They had been told by their doctor in Germany that radon is much more effective when it is taken in through the skin by water than through the lungs by gas. However, this is purely anecdotal.
In any case, I wish you the best. If you have anymore question, I'd be happy to answer.
Luigi
