As much as I want to keep Edge as my main browser, I have to stick with Chrome for this one. I really, truly love Chrome's way of pinning sites to the Start menu or pin in the taskbar, each with their own icon and opening as a separate window. That way I can have a tile to open Tweetdeck, one to launch WhatsApp Web, another to launch Jira (my workplace's task management service) and so on.
Firefox would be nice too, but I hate not being able to pinch to zoom on my Surface Pro 3 (it just zooms text and image elements rather than zoom in like a picture as Edge and Chrome do).