Category. I say this because you should really be categorizing your posts under specific categories so that Google can understand what your website is about (SEO).
The common wisdom (based on information from Google itself) is that you website should have 4 main categories. I would add that, for excellent SEO, you should also have 4 sub-categories for each main category.
Make each main category relevant and related to the main topic of your website. That is vital for good Google ranking.
Happy to answer more about this is you want.
Kevin.