I'm personally a fan of attention schema theory. It's based on the idea that consciousness emerges from an advancing capability to create models of both the external and internal world. For me, it scratches a couple itches. First, it's not an all-or-nothing evolutionary gamble, but develops in steps and each step has advantages. Second, it seems pretty well rooted in neuroscience and psychology, rather than relying on handwaves like "all matter has consciousness".

Here's a couple articles from Michael Graziano, the founder (discoverer? namer?):

https://www.nytimes.com/2014/10/12/opinion/sunday/are-we-rea...

https://www.theatlantic.com/science/archive/2016/06/how-cons...