Tom,
My experience with "hobby" magazines is that at some point they all have to start "recycling" because there is just so much that is new and because new readers need the information that "old hands" already have. Hence, most of the magazines have the same stuff in them after a while...
However, there is one issue that I never miss: Skin Diver's Photo Annual. They have some of the absolute best u/w photos ever! In the most recent number there is a picture of a snorkler and a whale shark that is breath taking! Skin Diver is really inexpensive and that one issue alone makes it worth the price, in my humble opinion--which some folks do not seem to think is so humble!
I have not subscribed to Undercurrents, but have seen a few issues and it looks fairly reasonable. I let my subscription to Dive Training elapse because I did not find it more useful than Skin Diver.
Oh yes, this Board is an excellent source of info--and,I think, you get more varied opinions here because most of the folks are not on retainers, do not get perks for doing articles, etc....
Joewr