Welcome to Eorzea!

I don't think there is an answer to "best server".
You'll find a community on pretty much any server. If you want to see what free companies are advertising, the best places to check are the Worlds(Group NA/EU) section. That will give you a feel of how active recruiting is on each server and what groups are looking for.
In general, if you are looking for a community I recommend against the companies that just spam invite without talking to you.
You will also see companies shouting in the starting cities looking for new members. Just send them a tell if they sound appealing.

Our free company likes helping new players and we also have a number of people running end game content, if you are interested. We also have a mix of MMO veterans and non. Our key ideals are patience, teaching, supporting each other, and having fun. We're a wacky bunch.