For me it was first VLC without really knowing what FOSS was, then KeePass while getting to know a bit about it, and finally Thunderbird. What did it for me was just how good and bullshit-free they were, especially in comparison to paid competitors. They really are the best products in their field, proving the quality often behind FOSS software.
If media/publishing companies would just throw the exclusivity model in the trash where it belongs (and let DRM die too), then everyone could pay to see what they want on their platform of choice without this bullshit. As long as that’s not the case, I don’t see myself using these “services”.