I prefer sans serif on a typical resolution PC monitor. I might prefer serif on a high-DPI but only my phone qualifies, and I don't do much reading on that.

For electronic reading, it's no contest for sans-serif for me. Really the only time I find serif easier is with low font size (like equivalent to 8px on my monitor) physical books. And it can only help so much, some newspapers here go lower, and while not unreadable, I wouldn't describe their text as clear.

Absolutely serif. Sans for paragraph text is an abomination.