What does it mean the best in the context? To me is about possibilities, and efficiency.
Possibilities are available when your hardware runs all possible operating systems you want to target. If you are targeting mobile phones, iOS is a huge market and one you don't want to be left out. This means you either own a Mac Book/iMac or your run a Hackintosh. Android is not an issue as it can be develop in all major OSes (Windows, Linux, MACOS. Windows Phone is of course a Windows thing and you will need it but that's not a problem because there is no much you need to do to install windows on a regular PC or laptop.
Efficiency is about opening IDEs, running games at a good resolution, opening audio tools, 3d modeling tools (such as Blender) and compiling without wasting an awful lot of time. This of course is determined by things like CPU (Cores and speed), RAM (Quantity and speed) and disk (SSD or not) among other factors (GPU is also very important).
Another thing to consider is the screen quality. In game dev you don't want to be missing details and pixels from the games you develop and play. You want to capture and transmit to your players the most vivid images, and without a proper screen this is not going to be an easy task.
Now, if you ask me, the only platform that comes with all these requirements by default is the Apple products. They are great hardware, which is a pleasure to touch and that perform very well in most of the circumstances. Of course this comes with a cost, which is the price, if you are fortunate of having access to one of this then you are going to be working to in my opinion is the best PC/laptop for game development.