Paint the slick side. The rough side will soak up more paint and you may
have some flaking of the wood slices as the paint soaks the board.

For the naysayers, I built a small storage shed in 1990 using OSB as the
finish siding, primed and painted it once in 10 years. It is still going
strong.



Thanks for all of the input. When I get some more done, I'll post some
pictures. I went with the smooth side out. It's working great. I
talked with some construction dudes and their assessment was that OSB is
as strong as plywood and in the hot and humid midwest, it handles
warping better. Who knows though. It's a lot cheaper at this point in
time probably because it's surpassed plywood in sales in the past few
years. Time will tell...
Ols