I like the concept of all three. #70 It caught my eye instantly, did you use te letters in fit? I see the I and the T but the F? #69 nice but ordinary #71 Like the icon which can be used alone and still represent the medium.
There is an F in the logo, you can see it on the left half of the logo (left arc of "T" along with the bottom -left half of the circle- but I have break the "F" with white space, so it didn't appear directly)