I had the same issue. Living in Kansas puts me right in the middle. I just compared the differences that I've come across in past games and real life. And looked at what information has been provided on the servers.
First and most important is server location and ping. West US servers most the time are stationed in west coast city like Los Angeles. East US servers often placed more central to the area, like Chicago. So midwest states should in theory be closer to server on US east and have slightly better ping.
Second is the people. Looking up some numbers shows more people living on east side of US compared to west side. So chance for higher population on server.
Thirdly, information provided so far about each server. This is going be based on one's personal opinion. Looking up info about the kingdoms and map for each server. I myself like the names of US west kingdoms more. Plus I like that there is more kingdoms on west. The map for US east was the exact one I voted for.
Conclusion is that the difference between the two is small. But with this being a action mmo with no tab targeting that i know of. Good ping is a must. This is a player driven mmo. So higher player population is better. Kingdoms and names can be changed once I've conquered the world. I had already selected my server before the map vote began. But the server mindset seems to be in line with my own. As the map i voted for won. So US east was the way to go.