System fonts are often overlooked, but they come with a massive list of advantages: environmental, performance, data cost.
using system fonts like Arial and Times New Roman instead of web fonts cuts down on HTTP requests, reducing the amount of data transferred and ultimately reducing CO₂ emissions.
The top 5 fonts given by Iain are: Georgia, Charter, Palatino, Hoefler Text (Apple only), and Segoe UI/Roboto/"system" i.e. the main UI fonts for each OS:
font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, Helvetica, Arial, sans-serif, Apple Color Emoji, Segoe UI Emoji; /* Only supported on Chromium-based browsers and Safari */ font-family: system-ui;