Do pages. They were the clear winner for me. I believe the reasons are very logical:
Posts are intended to be short term - for immediate consumption.
Pages are static, and they are there for the long term. If you are pitching something, then surely you would want that on a static page.
And then you can always add posts to support each page (as separate posts).
It's like one of those everlasting debates that never get settled. However, I will say this...if you know who Yoast is, then you know that he's a top authority in the seo/wordpress professional crowd. He says to do pages as well here: http://yoast.com/articles/wordpress-seo/
I make a category page, then pages within the category, and then use posts to support a particular page or the category/page itself.
I would expect that posts could rank, but I'm using them to help the pages rank. So I intentionally avoid trying to rank the post.