Almost every server suffers from at least one of these problems.
Free to play = lots of kids and assholes.
All f2p games suffer from this unfortunately.
Tons of servers have started going with ptw shops that give max gear and or gold, creating complete imbalance in the server and totally destroying the in game economy. Not a penny ever actually goes into the server though..
Some even just pull the latest stock trinitycore, hype it up with lots of promises than add a p2w shop and collect cash until the server dies off.. Then do it again.
Fast leveling = total noobs trying to be "hardcore raiders" anything over 2x rates seem to be plagued with this problem.
Massive population = you get literally every kind of person playing, the hostile and toxic players being most noticeable and vocal.
I stopped playing on 3 servers so far because of "guildies" and pug raiders harassing me after getting on vent with them, all on massively high pop realms where gm's outright refused to do anything about those players. Super high pop realms are total cesspools with a few decent people on them.
Once a server gets a name for itself and lots of fans, they tend to slow down or even stop development and start making up reasons why random easy fixes are never fixed.
Some examples: nost's no gathering node problem that lasted like.. A week and a half or so. Or dalarans many reported and "looked into" but never fixed bugs.
TL:DR: there are no wotlk servers worth playing on right now. Unless your an asshole of course.
I seriously wish I had the time/money to actually host a server myself.. People loved my lineage 2 servers years back.