Speakers. FS are at the bottom and FV on the sides. They are better on the FV, but they improved them with the FS13 compared to FS12 series. Other than that, I think the higher number FV have PiP, and might come with headphones.
For the price, I'd go with the FS13, unless you really want PiP. It has the same image quality, and TV speakers will always suck anyways compared to even a cheap pair of bookshelf speakers, so FS13 is a better value IMO.