I recommend Turtle as well. The extra content is generally really good as well. Fits pretty well into the world and makes levelling a new character really fun.
What's also cool, for an NA player, is that Kalimdor and Eastern Kingdoms have different time zones. So you don't have to play in eternal night even though it's an EU server
Turtle wow is probably one of the best and most populated Hardcore(1.12) servers around. It is EU based but i think it always has a few thousand any time of the day
Turtle wow is great. I play non HC myself, but there is definitely a big HC community there. They also created some new lore friendly quests and areas as well as a lot of of good changes,
Another vote for Turtle WoW here, they have a HC scene that seems pretty robust. I gave it a shot once but am not ready for the frustration quite yet. I am doing the Slow & Steady challenge myself right now, which gives 0.5x xp and in addition I am doing the challenge that doesn't allow rested xp and I am having an absolute blast. The server is alive at all times, I've yet to jump on and not see a few thousand people online at least.
Private servers are cool. Gives a feeling more akin to the old game back in the day. I like them.