I do not have a favorite program. In fact MYSELF I never really follow a program. I use programs for clients (but even then I do adapt it depending on what I'm seeing in the gym).
I personally use a general structure and have a goal for each session. I pretty much know what loading schemes I will use on a given day but depending on how my body feels and responds to training I make modifications in the gym.
Obviously I can't do that with online programs. The online programs all work very well and are based on strategies that I use(d) with clients and athletes. But I can't say that I have a favorite one.
And I never PERSONALLY go back to a program ... mostly because I don't follow a strictly structure program. I look at training from a problem solving angle, not a programming angle. I have a problem to fix and work on at every session, I build the session to solve that problem and adapt it depending on if the selected strategy is working or not. Because of that I rarely train the exact same way for a significant length of time because if I know what I'm doing my "problems" get solves and I focus on something else.
I know it's not the answer you want to hear because you are likely looking for a cookie cutter approach: the program that is sure to give you optimal results (most people who are attracted to a highly structured plan are attracted because they are insecure about what they are doing in the gym). But really that's not how I work. And the programs I design for online publications are normally designed as a short or mid term approach to fix a certain issue or accomplish a certain, specific goal.