I'm sure you'll get a variety of opinions!
If it's a small busy print, I've pieced down the middle. Some people frown on this because they say it puts more stress on the seam (from the folding maybe?). I've never had a problem with mine.
If I'm using a large print and have enough to match (as close as I can), then I might do that. Sometimes I'll use a strip of another fabric between so that I don't have to match if I don't have extra. Sometimes I do this and use up some of the blocks/fabrics from the front just to be decorative.
You can also seam both sides, cut one side down the middle, which leaves a full width in the middle and 1/2 on each side.
They all look fine. I think it's a matter of preference.