For me, there are four choices that really make sense. It makes sense because I've used them in one form or another. Also, all these frameworks are responsive by default so they support mobile development also not just standard web.
- MetroUI (and Office-UI-Fabric) - This is for those who like tiles (MetroUI). Fabric for web apps that look like Office365 apps. You don't have to be knee deep in building Window apps for web and phone to be using this - ie. You don't need Visual Studio or have a pricey WinDev account. It's open-sourced - Surprise! Surprise! It's built using Less; Curious though, no Typescript.
- Foundation by Zurb - Foundation is staple for those rabid SaSS fans and unlike the first two, this framework comes with everything even the kitchen sink. Heck, you can even make your own plugins. The strength of Foundation is its more malleable than Material or Metro but that's offset by the fact it's also has more moving parts. Testing much?
- Bootstrap - Twitter Bootstrap, the preferred frontend framework for the design impaired developer. Popular (maybe) and easy-to-use (arguable) it's not bad looking even if you're just using the base CSS. Sure, you can customize it with your choice of SaSS or Less but if your in a hackathon you just don't care and use a theme from one of many websites making free bootstrap themes like this one.