I subscribe to both. They fill different niches within the already niche-y aquarium hobby. TFH is a more general audience magazine, with a lot of nice advice columns on different aspects of the hobby. For instance, in every issue, there's a livebearer column, a discus column, a general cichlid column, a planted tank column, and Josh's (great) column on bottom dwellers. There are also big features on collecting trips, aquarium (the touristy kind) visits, and species-specific profiles. There's also the saltwater content, which I don't really read, since I'm not into that part of the hobby. I like the nice photos of the saltwater fish, though.
Amazonas is more scholarly, and some articles can almost read like journal articles. If you're a member of any of the national fish clubs, like the American Cichlid Association, or the American Killifish Association, and you get their quarterly journals, that's what a lot of the articles in Amazonas read like. They're way more in depth on species profiles/husbandry. Each issue tends to focus on one specific type of fish (bettas, earth eaters, shrimp, etc.), with several articles on that one topic.
So both are enjoyable to go through, but like I said, have their different focuses. Sometimes my eyes glaze over at how technical some of the Amazonas articles are, and sometimes the TFH articles can be a little basic. But all in all, I learn a lot from every issue of both. Both also feature great photography. I used to get only the digital versions of both, but I decided that I like having the print versions, so now I get those. It comes out to about $5 an issue for a subscription, which for the wealth of information they provide, I think it's worth it.