I think most of you tried to change the realm they play on but ended disappointed and at the end returned to their old ones. Here are some sites to help you decide the realm thats perfect for you :
WarcraftRealms.com - WarcraftRealms.com - This is the first site you check. Is displays the A:H ratio, number of players and
more... But remember its not very accurate but it should give you some info.
WowJutsu: World of Warcraft Guild Rankings: All Realms - A great site that can help you a lot. You can look at the guild
rankings so you can see how much is the raiding part developed.
SK Gaming | Global WoW Arena ranking - Here you can check the PvP ratings of the realm you think its good enough to replace
your old one.
I hope I helped, if anyone knows some other sites pls post them.