A warning about the 14 day trials: It's very limited. The character is unable to communicate easily, is level locked, can't have more than a few thousand gil, can't sell stuff on the AH, etc. The 14 trial can give you a small taste of XI's in game mechanics, but honestly there isn't anything particularly interesting about how the game is played, especially at low levels. (You hit stuff, you get your *** kicked by a rabbit, you eventually grow strong enough to kill the rabbits, you learn new skills, get better gear, etc. Same as any other game.)
The free trial will not show you XI's real strength, which is a deep and involving storyline with five expansions and lore so in-depth these days that it will take you six months just to get through a chunk of it.
I'd recommend keeping an eye out for the inevitable sales and price drops on the latest Ultimate Collection, which includes all the expansions. Right now it's $40 but when it goes on sale you can probably snag it for half that, and eventually SE will drop the price down to $10.