I have had good experiences with an older ca. 2009 Ritchey WCS seatpost and a newer Superlogic post. I had read stories about the older WCS clamps slipping but it was never an issue for me. The Superlogic post has an even nicer clamp (shared with the new WCS posts, too) that let's you set everything exactly where you want it then tighten it all up. Quite light (<150 grams) but not the cheapest option out there.