Which typeface (font?) to use and why

The 10 Most Popular Web Fonts of 2015

Ref: Choosing the right font

Contrast Ratio: Formula W3C

Email constraints:
Mailchimp says
from Bloomberg
Jan Constantin – Smashing mag
** StyleCampaign

Type+Place: Type Inspired by India
from Wanderlust Designer: On Typography

from keycdn.com Case Study – Analyzing Web Font Performance

Core web fonts

10 Web Design Tools to Discover Beautiful Fonts for Your Next Project

21 Stunning Serif Fonts for the Modern Website

Examples:
One Kings Lane
Oribe – for headings
www.etsy.com