According to here, it seems like the visible portion of lightning comes from the ground up; however I watched some slow motion YouTube videos, and it is clear that the lightning appears to be traveling downwards.
Also here it claims the visible part of lightning travels down:
Lightning goes both "from the ground up" and "from the cloud down". The first part you can't see starts up and goes down and is called a "Leader", leading the trail of the transfer of charge. Special cameras can track these. The Return Stroke actually propagates up the channel, and is the light that we see.
So how does one reconcile the fact that generally speaking people see lightning as going down? Initially I thought the brain may misinterpret the image somehow, perhaps since lightening is traveling so fast. But in the slow motion YouTube video the lightening is still traveling from sky down.