In Guild Wars 2 WvW there are Ranked Servers, then there are Mercenary Servers. Each come with distinct advantages and both have a reason to play on them. Here's a quick look at the differences between these two server types.
These servers have been ranked in the top 12 for WvW and carry the primary name of the battlefield. They have organized server meetings, expectations for builds and character classes when grouping, and tend to have some of the most competitive fighters in the game flocking to them. These servers are great to watch your realms progress through the ranks but also suffer to server drama that tends to crop up when guilds transfer in and mess with the chemistry servers have in place.
These servers are among the bottom 12 servers and thus have no rank bound to them. They are paired with other servers every 8 weeks based on their population. This lends to a very organic WvW experience with changing foes and changing allies on a regular basis. These servers tend to lend themselves well to new and learning players as they are able to play along side some of the best in the game and learn from them before their paired with another server. This creates an environment that is great for learning and getting the hang of things. There is very low server drama on these mercenary server as most of the competitive nature guilds have transferred to Ranked servers to compete in the server ladder.
You can see the current rankings at: https://leaderboards.guildwars2.com/en/na/wvw
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