The reference font for the body text of European proposals is Times New Roman (Windows platforms), Times/Times New Roman (Apple platforms) or Nimbus Roman No. 9 L (Linux distributions). The Roman family is from a pre-digital age and has well-recognizable features.
Is it the best font in terms of readability? On the one hand, there is a tendency to move from Times-type fonts to plainer fonts, like Calibri. On the other hand, many studies (with controversial results) account for aspects like Dyslexia, typeface anatomy, and Display vs. Print. The effect of font choice on readability and compression on big numbers seems small or insignificant. However, my point is that a proposal must be clear to a few reviewers, who might have difficulties understanding the proposal due to age, Dyslexia, and colour vision deficiency. These few people will have some feelings about how the text is formatted. For that reason and also because of my artistic education in caligraphy, I have been looking for and playing with font combinations for a long time. Here is what I have tried and liked.
1. STIX two and Source Sans form a pair of Serif and Sans fonts. STIX two resulted from a collaborative effort from the most prominent academic publishing companies. Its predecessor (STIX one) has exactly the same metrics as Times New Roman. STIX two is somewhat bigger, which is not prohibited by the EU funding agencies. The main benefit of using STIX fonts is that these are mathematical fonts and, thus, can be natively used in MS Equation Editor (instead of Cambria) and LaTeX (as XITS or STIX2).
2. An excellent substitution for Times New Roman is Zilla Slab – a unique font by the Mozilla foundation – which has the same metrics as Times New Roman, is a Sans font, yet looks like a monospace one, does have features of a Dyslexia-friendly typeface, and looks great in print and on screen. It is freely available from Google fonts. It can be used with Times New Roman (or similar) as a pair of Serif and Sans fonts.
3. Libertinus Serif + Gill Sans is my favourite Serif and Sans pair. You can see Linux Libertine in the Wikipedia logo. Gill Sans Nova is commonly fond in the University of Tartu (Estonia) press. Although Libertinus Serif has an original Sans counterpart, its combination with Gill Sans looks most natural. I love Libertinus because of its amazingly looking ligatures, and it is also compatible with MS Equation Editor and LaTeX.
PS One can play with fonts in the EU projects to make their proposal more appealing. Like Estonian grants, I prefer calls, where applicants fill out online forms without changing the text appearance. Of course, the text looks ugly due to nasty line breaks, horrible chemical formulas and mathematical equations, and poor typography. Still, the competition is more fair because everyone is in the same conditions.