Got a Druid to 100 before the season and a Rogue into the 70's with Barb and Sorc to 50. Barely played Necro as it has never been my type of class though played them all in D3.
I enjoy the Druid and Rogue the most and probably lean to the Druid because I like being a bit tanky since I'm not really that skilled. I have tried three different Druid builds overall and they have all been fun in their own way. I feel like the Rogue is similar as far as the build variety.
My season Druid is in the 70's. With the Aug 8th patch I may want to play Sorc as I always enjoy chain lightning type builds and that is getting some positive changes that may be worth trying. Originally planned to go with a Rogue next.
Anyway, I started the season with Lightning Storm after Pulverize before the season. I then at level 50 switched to the seasonal poison creeper landslide build. I should have just started with it since it is just a seasonal build. Plan is to get it to 100 and then start another class.
I think in future seasons I may focus on builds for classes that are only for the season or appear to be. But if I had to choose so far I really enjoy Druid the most with the Rogue a close second. Hoping the changes to Sorc and Barb elevate them as well.