Looks like they recommend concrete on all posts. A local dealer carries Bufftech at around $12/foot or $20/foot installed. Lowes carries "freedom" (whatever that is) for around $7/foot. Not sure I can justify the price difference between the bufftech and the lowes fence. Found some Bufftech online for around $10/foot but shipping cost is an unknown. The Lowes sections come preassembled too.
My only concern was I've heard folks say their vinyl was damaged by snow plows shooting ice chunks through them. The Rails would probably just fall out if hit, but the picket is screwed to the posts so something will have to break. I suppose it could break wood too, but it probably isn't as brittle in the cold.