You cannot classify them into 'old' and 'new' servers, it is a gradual thing that the server ages. The older your server when you start, the further you will be behind the top teams. The only con will be that you will face much better teams in the Cup, so it will be hard for you to win it, you can see my best record is still only Top 16 after 15 seasons. Other than that, it's a really smooth ride, plenty of 5* players at the lower leagues so you can take your pick.

Newer servers are just the opposite. If you are near the top, you will win the Cup easily, but 5* players will be hard to come by, and there will be huge bidding wars whenever one pops up.