Pulling down is always easiest, feeding can go either way, but feeding up IS a little easier (especially when working alone).
When running PVC outdoors or in unconditioned areas, remember the expansion and contraction is tremendous. In most areas, hot days to cold days exceed 100 degrees, and an expansion fitting is required for a 10 foot or longer run when solidly connected between boxes. To avoid using expansion fittings, I use 90 degree bends on the ends of runs and two foot long risers to allow for the movement of the pipe. Also, use only PVC straps, which are designed to allow the conduit to move.
