Rogue/Knight is decent for siege, as is M/P and W/K.
As a PvP server, Grimdal as quite a bit less players compared to PvE servers, and most of the population are max level, so the lower level zones would be a bit empty.
There are usually free world channels in every server though, which you can join in and chat with. Of course, there's also many guilds willing to help out newer players