Typefaces for official correspondence

What font do you recommend for official correspondence? I would like to try and convince my work (a State government agency) to switch from Arial (10,12 and 14 pt, with fully-justified paragraphs!) to the most reader-friendly font/layout possible.

I know from reading your books that serifs make reading much less of a chore, as do left-justified paragraphs, but I’m not sure which font would be the best. I have personally made the switch to Times New Roman 12pt for my writing at work but of course nearly everyone else is toeing the line and using Arial.

I note that the US State Department has recently switched from Courier 12pt to Times New Roman 14pt, refer link for news report, so maybe Times New Roman is the way to go?