The only esports I've spent any sort of time watching is League and Hearthstone. Hearthstone might not be considered a real esport yet, but it sure is dang close. Even though the game is RNG based, its still great seeing the best players in the world go head to head and just learn from their lines of play.
If I had to pick, I'd go hearthstone, just because I know the community a lot more than I do League. The LCS is entertaining to watch too, but I haven't learned much about the teams.
League of Legends is my favorite esport to watch right now. It's my primary game at the moment however so that might be influencing it. I have watched some of the CSGO tournaments but when there was the case of some teams hacking I kind of just find it not as exciting to watch. That and I go and play CSGo and the bs hit detection makes me want to break my keyboard so I kind of gaveup on that scene too.