Hi and welcome or welcome back! Not sure how you got here.... But in terms or server choice if you want high population from what I have seen Fingal, Epona or Arawn are all well populated servers. Epona is the only free server meaning that they roll for drops and there is minimal clan competition, the other two are both dominant clan servers.
Regarding getting gear easily, it depends on what sort of gear you're thinking of, for example you can easily buy raid gear on Epona with enough gold (chests sell for around 25k there) however quest armour is harder to come by and you will spend much more time camping bosses. However, with the dominant clan servers you will have an easier time getting quest armour but raid drops can be hard to come by or need to be earned rather than bought.
Whatever choice you make it's a great game and on any server you can find some amazing people to hang out with. So good luck (hope your GCSEs go well!!) and maybe see you in game