Let me preface this by saying that I do not have a subscription.
If I were going to subscribe it would be to read their articles, rather than see videos and modern content that is available on the net and tv news. I prefer e-ink screens for reading, and thus I would not purchase the i-pad version. Further, I suspect that the ads on the i-pad version would be more obtrusive as they can be in color and have video.
The Kindle version seems to include the ability to get the journal on the i-pad. I assume the i-pad version also includes the ability to read it on the Kindle.
Thus, I think this is really a thread about what you would like to read it on.