Classic Era servers are mostly unpopulated but Whitemane seems to be the best choice if you don’t want to play SoM.
Blizzard simply does not have the manpower allotted to Classic to push out “new” content. What you are going to get is half thought out changes that affect the game drastically and ruin the player experience.
Hopefully SoM is a nice experiment that shows devs that Classic Era should have a fresh server and to stop trying to “make Classic better”.
This is where having a Classic Era fresh server up would be awesome. It could funnel all the players that don’t want to do a rushed season, would grab private server players, and appease the Nochanges crowd.
Merge all Classic Era current servers to 1 PvE and 1 PvP. Create a new server for CE that is designated as the “fresh” that resets 6 months after Naxx release where you can then transfer off to an existing CE server, similar to SoM. Do this every 18-24 months, minimal effort and easy profit.