Well first off, are there more than 1 TLE servers? I don't know what they are but I'm assuming there are more than one because I heard one named Kaladim and one named Fallen Gate. Am I wrong? Secondly, which server (not expansion pack released) is the newest released server? I want to join a server as near to release as possible. I started on Kaladim last night and noticed there are already level 68 people on the server. That puts me way behind in joining a guild to do raid content from the beginning.
Kaladim is newest with population. There is a dead pvp server too. KoS expac unlocked on it this week, so people are going from 60 to 70 currently. Server has existed for 8 months(?) now. 4 for base game, 4 for DoF, and now KoS. I suspect you're unlikely to find any raiding outside of the 'end game' content unlocked now.