Stopped reading here. No, it's not that. It's the community itself. Warmane is and will remain the biggest WotLK private server, it just has an incredibly ****ed up community and no, I'm not saying this because "the large amount of players make me encounter a lot of *****s". Playing and enjoying the game outside of a guild is next to impossible. Very often - even when inside a guild. Try it and you'll see.
Whether Warmane is the best... this depends solely on the continuous work of the developers. Right now I would say "no" on that, sadly. inb4 "but we make our own scripts and don't take from opensource". Over the last two months since I returned post-Moltdown I've reported more than 20 bugs on WotLK (go check the bugtracker with my name if you don't believe me), only one of them has been fixed because I listed it as an "exploit" (and it took just several days too, perhaps I should list all bug reports like this, hmm?).
Edit: wtf is wrong with Sapphire? I like people who are straightforward.
Edit2: I have to agree with willardnigma's opinion here. He's right on many points. I've said it before - you guys were indeed #1 in the past in quality too, and you took pride in it, but if you want to remain the #1 server you HAVE to keep running alongside (or even ahead of) trinitycore emu. Just look at the amount of working scripts, movement systems, collision etc. which have been working on these servers for years and which still don't work here. As willardnigma said, the quality lead has been slipping away for you over the course of the last couple of years. And don't take this as bashing, please. I want to stay on Warmane, I really do. There are still a lot of quality players and guilds here worth staying for. But I also want those abovementioned things to work, like they do on many other servers already.