They're actual SWG Credits people that can turn out to be some of your very close friends.
There are guilds that always war; swag credits guilds that sometimes war, and guilds that never war. None of these choices are bad, just based on a different personal preference. Does the guild talk frequently/get along well? This may seem like an odd question, but it is much more enjoyable if your fellow guild members are very active and are willing to talk and party basically all the time. It can be very boring when no one is talking, so you probably want to pick a guild that gets along very well with each other so there is always an interesting conversation to stick yourself into. After you join a guild, try to add your guild members as friends, and build relationships with them. They're not just a green title above your head; they're actual SWG Credits people that can turn out to be some of your very close friends. Getting to know people is a really good thing in a guild, because they will begin to trust you and you will move up in rank.