I pretty much always start in the middle. I pin basted and work on my HQ Sweet Sixteen and I find it easier to work on the edges if the middle is done. That said, I do a lot of FMQ rather than SITD or long straight/wavy lines. On those I do go edge to edge but usually start with a middle line and work one way out and then the other.
It really can just be personal preference, how you want to baste and quilt.