I’m more familiar with “meh” than “feh,” and I first saw “meh” at another MB years ago. Not that it couldn’t have come from the Simpsons. Just sayin’.
I’m all about the “feh.” Never heard “meh” outside these boards. It reminds me of a hungry goat.
Today’s For Better or For Worse uses “feh.” 
“Meh” comes from Simpsons. At least that was the first place I every heard it. From snpp.com:
Homer: Kids, how would you like to go to … Blockoland!
Bart + Lisa: Meh.
Homer: But the TV gave me the impression that –
Bart: We said, “Meh!”
Lisa: M-e-h, meh.
– Intense indifference, “Hungry Hungry Homer”
Count me with those who’ve never used “feh.”
I’ve heard “Meh” used everywhere: school, work, on several different message boards and web sites. I’ve even heard it used in a song.
~Tasha