I play on gorgonnash. Blizzard has this rated as a low population server. I have a lvl 45 character and am tired of wating in horrendous queue lines in order to pvp so I am looking for a server that is medium pop. I went here to try and find the ideal server so I sorted the server by population and gave it a whirl.
After taking in all the numbers it looked like black rock was the way to go. According to this website blackrock has 20,006 for the 4th highest pop server. But when I went online to make a new character blackrock is rated low pop.
I've found this to be true for many of the servers listed here. Anyone know what the deal is?
the accuracy of the stats on the site
The total population numbers reflect how well people are doing on the server submitting data rather than actual population relative other servers. The reason for this is simply that a lot of servers are very poorly mapped, and some are thoroughly mapped 
If you want to get an idea of actual population you pick a server and then you check the activity numbers, that is the actual number of people logged on for either faction at the time you play. Blackrock for instance is a good choice for aussie hours since it has very high population during aussie prime time (being the primary unofficial aussie pvp server).
I don't know the hours you play so I can't give more specific advice but in general PvP servers like Warsong and Archimonde have very high populations at peak with queues in the 100's. Other servers with fairly high population but not close to being capped (less lag, no queues) include Bleeding Hollow and Sargeras. I do suggest check each server for population at the times you normally play though.
Blizzards server status page gives an idea too and should be accurate but unfortunately it seems to be too buggy for use really, too often I see servers tagged as low when I know from doing census at the same time that they are packed and the other way around.

If you want to get an idea of actual population you pick a server and then you check the activity numbers, that is the actual number of people logged on for either faction at the time you play. Blackrock for instance is a good choice for aussie hours since it has very high population during aussie prime time (being the primary unofficial aussie pvp server).
I don't know the hours you play so I can't give more specific advice but in general PvP servers like Warsong and Archimonde have very high populations at peak with queues in the 100's. Other servers with fairly high population but not close to being capped (less lag, no queues) include Bleeding Hollow and Sargeras. I do suggest check each server for population at the times you normally play though.
Blizzards server status page gives an idea too and should be accurate but unfortunately it seems to be too buggy for use really, too often I see servers tagged as low when I know from doing census at the same time that they are packed and the other way around.
Also, Blizzards page is supposed to show people logged on at the time you look at the page. That means that if you make a character at say 3 pm EST on a server it may say low population but if you go back and check later in the evening the same server might be high population since most people play in the evenings.Yet another reason to check the activity numbers carefully for any server on this site when choosing a new server.