If you want to enjoy extra bonuses and an easier head start go for a new server, but like said above, the pupulation isnt usually the best.

If you want a super active server join an old one. You can still play pretty well and you'll only really lose in pvp group functions but things like sage world tend to be more balanced with a higher volume of players. Just accept the fact that unless you will top up like crazy you wont reach the top anytime soon and be sure to stay on top of your gear and you will easily beat the level rushers. Slow and steady wins the race and is the key to enjoying this game in an old server, unless you feel like rushing to level 70 with only 10k power then getting beat by a level 50 with 13k is enjoyment. But its your call.