The Vivaldi browser, which is built on Chromium, works on both Mac and Windows but not iOS yet. It takes any Chrome extension and has features like built-in webpage screenshot capability, note-taking which can be associated with a URL and many customization options. Aside from that I use Chrome, which is pretty fast and syncs very well with all of my Windows, Mac and iOS devices.
The upcoming version of Microsoft's Edge browser (built on Chromium) sounds very promising, with the ability to accept all Chrome extensions in addition to Microsoft-specific features. Edge is particularly interesting because it also works on iOS devices and synchronization between all platforms should be possible.