Blizzard will be launching a new service known as "Wow Classic Season of Mastery" in the next few weeks. These servers will be like an opportunity to start over with basic (no TBC content, just 1-60) with some twists. The twists are "leveling can be faster" as well as "raid bosses can be harder to beat." Wait a few weeks to develop a character, if you only want to play classic content and not the burning crusade stuff**.
The choice is entirely dependent on what you want, but yeah If you are looking for that type of first-time leveling experience in which everything feels fresh , then Season of Mastery is the ideal choice. The majority of vanilla servers, if they are not all dead. It's mostly used for people to keep their character as an artifact in the moment. TBC is okay , but getting into an organization might be a bit more difficult since people have already completed a significant amount of the way. As soon as it's available I'm going to try to join SoM.