I began using Bohemian Coding’s Sketch almost exclusively for web design a few years ago. It’s lighter and faster than Photoshop, has a stripped-down set of features that meet my needs, and has a workflow that allows me to get work done faster. And at $99, it’s quite affordable (and I do like that I pay once, rather than every month).
I have one source of irritation, though. I run Sketch on my work machine and my home machine (which is permitted by the EULA, of course). I ran into an issue of plugin parity between the two machines.