Gonna assume you're talking about NA if you are from Dynamis DC. If you're traveling DCs, that means you can only play Casual CC or Frontlines. You can't play ranked CC anywhere else and Rival Wings only pops during discord-organized events and they rotate data centers.

Aether's CC ranked scene is currently dead, but it probably has more Frontlines games. However, I mostly hate Frontlines on there because I think they have both the best and the worst players, which makes games pure RNG if you get the good players on your side (usually in premade groups). Same with casual CC : both the best and the worst players at the same time. Games usually become pretty decent very late at night, but they stop popping when it becomes interesting.

I much prefer Primal for PVP. I find games more competitive and players to be pretty decent overall.

It's a matter of personal preference, but if I were to rank the NA DCs according to fun, it would be Primal > Crystal > Aether. Dynamis is still too new to be included and doesn't currently have active PVP. If we're just talking smaller queue times, it's probably Aether, but the wait times on the other data centers are not long either.