Depending on what type of mmo you want there are different choices. For a pretty standard one WoW is a pretty good choice, you can even try out the starter thing up to level 20 for free. Wildstar feels like WoW with a more involved combat system, which isn't always a good thing. Also supposedly you can buy your monthly sub with ingame money if you earn enough. FFXIV is the one i'm currently playing right now, while it's somewhat of a standard hotkey style mmo it does have a pretty strong focus on story, which is a very classic FF story, so if you like FF that's something to keep in mind. Oh right, there's also a free trial available, or if you want one of the people in the guild right now can refer you as a friend for a trial.
Also whatever you decide to play you may want to check if there're GB guilds. FFXIV currently has a pretty active guild and i believe some people are restarting the WoW ones recently, couldn't tell you about the other mmos though.