Check out the populations of all the servers; ironforge.pro tends to be the main resource for this.
Then check out the pinned thread on this forum, Wrath of the Lich King Classic Discussion, Character Transfers Update – May 1
From this list it looks like these are your options From Angerforge - To XYZ
This information may not be up to date. To confirm accurate information, you’d be best to log into the game. Select your server, Angerforge, then while on the character selection screen for Angerforge, go to the bottom left and click on the Shop button above the AddOns and Menu buttons.
Once you’re in the Shop, go to Services. Once on the Services tab you can click on Free Character Transfer and select a realm to go to there. If none of these realms look good to you via population or friend location wise, then you may wish to opt to the paid Character Transfer.
Before transfering to any server, make a new character on that realm and check it out in person. Look at the Auction House, ask questions in Trade chat. Get a feel of what the environvment is like.
Best!