[Update #2]: I'm happy to say that World of Warcraft: Classic has now been officially released and that the servers are practically overflowing with players!
[Update]: Blizzard has announced they will be adding a whole bunch of new WoW Classic servers on August 26th, right before launch!
Blizzard recently opened up World of Warcraft: Classic's character creation and gave players the ability to reserve up to three names per account. As you might imagine given the hype behind WoW Classic, the moment the servers opened up was also the moment some of them ended up getting filled to the brim with eager players.
In order to avoid hour-long queues and give players another chance to reserve their favorite names, Blizzard has now launched two additional servers: the Stalagg PvP server (EST) for North America and the English-speaking Gehennas PvP server for Europe.
I can't speak for the US server, but as of right now Gehennas is a medium-sized server while both Shazzrah and Golemagg are classified as full. So if you were worried about swapping to Gehennas because it might end up being a dead server, I think it's safe to say that's not going to be happening any time soon. Besides, the moment the flood gates open and everyone creates their characters on August 26th, pretty much every server is going to experience a massive influx of players, both veterans and newbies alike.
Whatever you end up choosing in the end, I wish you the best of luck with grabbing your favorite names!