Tempered glass is four times harder than regular glass, so using it as a screen protector for your Surface Book or Surface Book 2 seems like a no brainer. If you're wondering where to start, I've rounded up the best of the best right here.
Megoo's tempered glass screen protector (from about $23) comes with everything you need for bubble-free application, and the protector has cutouts for the speakers, microphone, and IR camera.
It's so thin you'll hardly be able to tell it's there, and an oleophobic coating will cut down on smudges and smears from your fingers. There are options for the 13.5-inch and 15-inch Surface Book models, so be sure to select the right one at checkout.
If you plan on keeping your Surface Book or Surface Book 2 around for awhile, this screen protector from ZAGG (about $65) comes with a limited lifetime warranty. If you break it, ZAGG will send you a new one as well as a return envelope for the old one.
It repels the oil from your fingers to cut down on smudges, and it comes with the tools needed for a bubble-free installation. Note that this works with 13.5-inch models only.
Compatible with the 13.5-inch Surface Book and Surface Book 2, Spigen's tempered glass protector (about $15) is a cheaper option that nevertheless has cutouts for the webcam and speakers.
There's an oleophobic coating to reduce fingerprints, and everything needed for a bubble-free installation is included in the kit. It also comes with a lifetime replacement warranty; if you break it, Spigen will send you a new one without a hassle.
Updated June 12, 2018: I've refreshed this list to ensure these are still the best tempered glass screen protectors for both Surface Book and Surface Book 2.