My choice for Best Open Source CMS for this year (and the one that will be my #1 recommendation in this category until next years awards) is the one and only, MODX CMS!
MODX is an incredible CMS that offers an abundance of features for those looking for quality software for free. MODX Revolution starts as a completely blank slate. Start from scratch, or use the Package Manager to download and install Add-ons, Core Extensions, Templates or even Content Pack Distributions.
As my choice for this year, when asked to offer suggestions for the best open source CMS, I will point to MODX. They will receive my recommendation from now until next year’s winner is announced.