Sorry, but there's no such thing as a perfect machine for AE work; the optimum machine for 4K work for feature-length productions would be different than the optimum machine if you specialized in making ads to be viewed on smart phones. So figure out what you'll be doing with this machine and then we can get more specific.
I will say this: AE generally works better on a Windows machine than on a Mac at this time; if you're an IT person who specializes in Macs, get whatever you want.
Some minimum specs at the moment would include at least 16 GB RAM, a big SSD for caching, fast processors (AE currently favors processor speed over the number of them), and a fancy video card isn't necessary -- you'd get the card based on your OTHER needs for the way you work, not on AE.
As Dave said, this is an entire can of worms and there is no such thing as a one-fits-all the best machine. Without exact requirements and workflow info this is going nowhere.
Regardless of workflow, you want a workstation, not a laptop. You will get much more bang for your buck.
Also, as others have said, Windows machines tend to be better choices than Macs right now. And that's coming from two people who used to use/love Macs...
In general, you want the fastest clock speed on your processor that you can afford. You want as many cores as you can get with that nice, high clock speed.
Ideally, you want 4GB of RAM per core of your processor - MINIMUM 16 GB of RAM, (but get as much as you can afford).
You want an SSD for your cache and a good-sized regular hard drive to hold footage, renders, etc.
GPU matters for Premiere and any third-party plugins that use it (like Red Giant Universe, Element 3d, Mettle's ShapeShifter, etc.), but not for AE and not for Cinema 4D (which comes free with AE these days).
Again, this is just some generalization. For more specific info, we'll need to know more about what you're doing.
Also, you don't need to take our word for any of this; read what Adobe has to say on the matter: FAQ: What computer and components should I buy?