Merriweather

Merriweather was drawn by Sorkin Type specifically to be read on screens, and every decision reflects that. The x-height is large, the counters are open, the stroke contrast is deliberately low, and the serifs are slab-like rather than delicate — all choices that keep letterforms intact when a rasteriser has few pixels to work with.

The result is one of the most reliable free serifs for long-form body text. It is the default on a great many blogs and reading apps for good reason: it stays comfortable at 16–18px over thousands of words, which is a harder problem than looking good at 48px.

The trade-off is that it is fairly wide and quite dark on the page. In narrow columns it wraps often, and as a display face it can feel heavy next to something like Playfair Display.