What is the most common font on different desktop and mobile devices. I need my website texts to have the same look and size on different devices.
This is a subject that could end up on discussions, but I'd say; considering the widespread use of Windows, the agreements that Apple has with Microsoft, the early versions distributed from Microsoft and the different ways to install fonts on Linux, that the best options, are the Core fonts for the Web from Microsoft. Specifically the Georgia and Verdana.
Roboto Family is upcoming widely used font.
Among the above, Droid Sans & Oswald seems to cover moderately among all the browsers.
All data are taken from Google Fonts analytics, refer it, change the filters & check it for yourself.
I would go with Open Sans as Oswald renders badly in Chrome(atleast for me).
On websites you have three main ways to specify fonts. You can specify fonts that are installed on a person's computer, you can use a font service to pull in a custom font, or you can pull in specific fonts you want.