I have gotten byo for almost 6 years now, and I used to love it. When I first got it, I purchased a few issues at bookstore, and then a friend of mine offered me a half off subscription. Basically, Oct to Dec they offer a buy a subscription, give one free deal so we always would split the cost. I started upgrading to a print and digital deal so I could have the issues available in case of fire, loan an issue out and never get it back etc. Additionally I could view the past articles online from past issues etc. This past Christmas, I signed up for the deal, and noticed in Feb that I could no longer access the issue digitally. Emailed to question why, and was told that I didn't purchase the digital issues, even tho I sent them screen shot of my subscription information, and now they have gone to digital subscription only online articles where before if you picked up a back issue, which they still sell, you would see a link in the magazine to a beer line cleaning article. You could then go on to their website and view that article. Now if you do not have a digital subscription, you cannot access theses articles.
I really do not know what their digital subscription gets you, as I refuse to pay them more money for what I thought I purchased from them in the first place. So to make a long reply a little longer, I would recommend the print version of the magazine, and if you can find a friend and if they offer the get one free for Christmas, i would do that route.
I have purchased a few zymergy issues, but I do not find it very useful. I like reading about different styles of beer with lots of recipes, which BYO provides, plus diy projects. Zymergy seems to be very lite on recipes and more on reporting on brewing competitions etc. Upside to Zymergy is some homebrew shops offer a discount if you belong to Zymergy, but the cost of the membership does not offset the savings to me since I really don't spend enough on qualifying purchases.
I guess the bottom line is which magazine over a 3 issue trial period offer you the most of what you are looking for.