I generally start in the middle and work to the outside. Then I turn the quilt and tackle the other half. Now some newbies mistake "middle" with "center" - For straight-line quilting I do NOT start in the center, rather at the edge of the center seam.
My quilts are smoothed and basted really well but I still have some shift in the sandwich. If I started at the side, I would need to work out a lot of extra bulk by the time I get to the middle. So for me it makes more sense to start in the middle and work outward.