Square, 10". I might choose a column with a larger base, say 10" up to 36", 8" above that.

Will you have a rail?

Thank you for chiming in! No there will not be a rail, but we will be planting shrubbery along the porch to provide a natural buffer. I also thought square columns would look best, but my builder & architect both say round due to the fact that it's a colonial style home. Apparently that's a rule? But I wouldn't even consider our home to be a true colonial...

place a chair on the porch and sit in it before you decide…This will help with the size and placement of your columns... based on your vantage point and view.

I would go square. I do not see colonial?? Go with your gut.')