for me its http://www.type-together.com/ and Bold Monday. Both have stunning design, and allow you to preview the font rendering, change size, leading, text, font style, opentype features, amazing. choosing different sizes and previewing live Rendering, is particularly important, for choosing fonts on Windows, to ensure the hinting is good, which it is for all their fonts, its excellent. https://boldmonday.com/ Another standout, design wise, stunning. Being able to preview how a font will work on the Web is critical I think.