This is a list of servers that you can order by population and such. http://xivsoul.com/

This also groups the servers by data center, so you can check it out. Aether and Primal data centers are servers with the majority of NA players, while Chaos is EU and all 3 are located in Montreal, Canada. http://na.finalfantasyxiv.com/lodestone/worldstatus/

P.S. Elemental, Gaia, and Mana are Asia; if you are considering those servers. These are located in Japan so you have less latency issues from the Eastern Pacific (such as our Aussie friends).