My reaction as designer is different. Today, UIs often get quite complex, and can contain at least few different sizes of the text. 1. Serifs often have uneven

My reaction as designer is different. Today, UIs often get quite complex, and can contain at least few different sizes of the text. 1. Serifs often have uneven stroke weights which make them actually actually harder to read in small sizes (8-15), since the thin parts start to breakdown. 2. Letterforms are more complex and generally create more "visual noise" or the texture of the text gets noisy since you have lot of points and ticks on the screen. I think serifs can work well on titles that are large, quotes, in print or simple ui like articles where you one column of text, mostly in one size. For UI, especially mobile UI feel like it can be quite jarring in any more complex app. Legibility also comes from the different factors of the typeface (x-height, open counters, distinct letterforms) not only from the fact that it's serif or sans serif.