Every one that I can fit in to my schedule. I'm a bit of an education junkie. Like Dale, though, I can't just sit and watch. That's where crochet comes in. Keeps my hands occupied so I can concentrate without getting distracted.
In addition to Legacy Family Tree webinars mentioned by Emma, I monitor multiple state genealogical and historical societies, the US and UK National Archives, the Family History Library, and various genealogy software vendors like RootsMagic, Legacy, FamilySearch, and Ancestry. Many of them have YouTube sites that let me watch later. I also "attend" conferences by watching their livestream sessions, both free and paid.
An easy way to get started is with the calendar at GeneaWebinars. I'll save you a seat.