Regardless of server, whenever a fight occurs between 20v20 or more, the lag hits hard. Some will disconnect as you will see the player standing there like a statue.
If you're EB, we usually own Chillrend and can earn some easy fights. Occasionally AD or more rarely DC will make a move, but generally don't get more than three or four keeps.
Thornblade is a slightly less-laggy populated server. All three play, but it is certainly not free from lag. Just generally less of it than Scourge. Was sieging a castle for over an hour last night until AD finally killed us off.
Scourge is really good, during peak times all factions are pretty much full. I tried to get on around 11pm cnt on Sunday night and had to wait in Qued position just to get in. DC generally owns a good deal of the keeps but EP makes a good push every once in a while and AD is always a nuisance.