I really don't think it makes much difference if you are machine piecing. I usually will press to one side if I'm doing 4 or 9 patches, but if I'm doing something like a hexagon (One Block Wonders) or any type of kaleidoscope or star block where 6 or more points come together, I will press open to reduce some of the bulk at the point. And with todays fabrics, if you are using a good quality quilting cotton, I really don't think it matters if you press to the dark or light. The seam is only 1/4 inch, and unless the fabric is really thin, most people wouldn't even notice if your seam was showing under the light fabric.
Best word of advice... try it both ways, with different blocks ( 4 Patch, Kaleidoscope or hexagon) and see which way you like best, and do what works for YOU!!!!