The answer depends largely on how you use a 2-in-1 PC. If you think you'll spend most of your time in laptop mode, and you don't mind spending more cash upfront, then go with the Surface Book. But if you use a 2-in-1 in tablet mode for, let's say, at least a third of your time – or if you just want to keep the cost down – then you'll probably be very happy with the Surface Pro 4.
Where you use it can make a difference too. When using the two devices on a desk, we prefer the Surface Book, thanks to its 21 percent bigger screen. They're both fine on lap, but there we prefer the smaller, less bottom-heavy Surface Pro 4.
As a tablet, we love the Surface Book's form factor. It makes for a huge slate, but feels incredibly light in hand: it's 9 percent lighter than the Core i5 and i7 Surface Pro 4, despite being a much bigger tablet.
But there's a very good reason that the Surface Book feels so light as a tablet: there's not much battery in there. Microsoft put two batteries inside the Book and only the smaller one lives in the screen. As a laptop, it has great battery life; but as a tablet, you can only count on an hour or two of use between charges (maybe more, but we like to crank the brightness up almost all the way).
That's probably why Microsoft is avoiding the word "tablet" when describing the Surface Book, and instead calling it "Clipboard Mode." We've all been trained to expect day-long battery life from a tablet, but a "Clipboard" PC? Nobody knows what the hell that is, so it can last as long as Microsoft says it does.
Let's rewind a bit and run through the two different form factors:
The Surface Pro 4 is like older Surfaces, where the device itself is a tablet and its laptop mode only comes into play when you flip out its kickstand and snap on a thin, detachable keyboard accessory. This makes it a little thicker and heavier as a tablet, because that's where its battery (and everything else) lives. But it also means its battery life is going to be the same no matter how you're using it.
The Surface Book, which is more like a traditional laptop, flips that around. Its larger battery and, in the higher-end models, discrete Nvidia graphics live inside its bigger keyboard base station. When you're ready to use it as a tablet, you long-press on a key (or just click an icon in the Windows system tray) and it will then let you slide its screen off for some "Clipboard" action. Until you do that, though, that screen is staying put.
Put even more simply, the Surface Pro 4 is a tablet with a snap-on keyboard. The Surface Book is a laptop with a slide-off screen. They're each sitting on opposite ends of the 2-in-1 see-saw.
Both include Microsoft's Surface Pen in the box. The latest model has great pressure sensitivity and palm rejection, and Windows 10 lets you do more without having the keyboard attached. When you need to type a little something and you're in tablet mode, no need to reattach the keyboard: just scribble your words using Windows' excellent handwriting recognition.
You'll still want to bust out the keyboard for longer-form writing, but for a quick search or email reply (or, in our case, even some article edits), handwriting will do just fine.
Build quality is top-notch on both devices. They have similar magnesium builds, and feel just as premium as any Apple device does. Microsoft was a little slow adjusting to this new world we live in, where high-end Apple products often set the tone for the rest of the industry, but now Redmond is making lust-worthy products of its own and playing that game as well as anyone – including Apple.
Screen quality is awesome on both devices, with the same crisp (267 PPI) pixel density. Text and images look razor-sharp in both laptop mode and tablet mode.
Typing is a pleasure on both Surfaces – both have snappy-feeling keys and big glass trackpads. The Surface Book has that thicker, wider and heavier base, but I love rapping out articles on the Surface Pro 4 just about as well. Consider this, if anything, a slight advantage for the Book.
Performance will depend on which model you go with. Our Core i5 review units benchmarked about the same in Geekbench 3, despite the entry-level Book having double the RAM. If you buy one of the higher-end Surface Books with discrete GPU, you'll get an extra graphics boost for games and graphic-intensive apps like Photoshop or Lightroom (though, for what it's worth, the Core i5, integrated GPU models of both devices handle Photoshop and Lightroom just fine). No models of the SP4 give you a discrete GPU option.
For most shoppers we'd recommend skipping the entry-level (Core m3) Surface Pro 4 and going with at least the second-tier Core i5 model. That m3 model is fanless, but it's also about 25 percent slower. We think the i5's raw power boost is easily worth US$100.
Our review units' battery life has been good, and our tests came out a draw for both devices. When streaming video with brightness set at 75 percent, they each dropped just 9 percent per hour. Just remember that's only for laptop mode on the Surface Book.
If we had to pick an absolute "better" device, we'd go with the Surface Book – I personally prefer its bigger screen and lighter tablet mode sitting on my desk – but the Surface Pro 4 is an excellent product in its own right, and once you take pricing into account the SP4 looks better and better. In many ways it's the same machine, just a little smaller, a little more tablet-y and more than a little cheaper.
Your question isn't just whether the Surface Book is better, it's whether it's $370 better – that's the price difference between the nearly equivalent Core i5/128GB SSD models we handled.
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