The absolute best computer depends entirely on three factors. First, the current release of AE always favors one OS and System Configuration over another. Some of it has to do with the GPU, some with the CPU, some with the memory and the system architecture. You will never have a system that is always the best performer because that machine changes with each new release of any software that taxes your system. Adobe products are no exception.
Second, the best machine is also dependant on the kine of work you do and the type of footage and other assets you use in most of your projects. Each machine and each OS handles codecs, formats, and frame size a little differently. The type of work you typically produce and the frame size and source of the footage you use also determine your ideal machine.
The last factor is the long-term cost of operation and reliability of your system. Every hour you spend fiddling with drivers and updates that can cause problems is an hour you are not being productive. Every time the machine needs service or repair costs you time and productivity. The trade-in or resale value of the machine, the warranty cost, the speed of repairs all affect the suitability of a system. I started on a Power PC Mac in 1994 when I first started using After Effects because that is the only platform it would run on. In 1997 I started custom building PC's while keeping my Mac and I almost always had both running every day. Some things were faster on the PC, others on the Mac. For a while, the best investment was a custom-built PC. That lasted until the Intel Mac was introduced. When I was running an Intel Mac I switched to HP workstations, then Dell and Alienware. I still kept a Mac. The Mac always took less maintenance and there were far fewer problems with drivers and updates. For a few years, every time I ran a Windows update AE and several other programs had terrible problems and I lost days of work trying to figure things out. For about the last 12 years I have been 90% Mac because the cost of ownership and maintenance was far less than the cost of ownership of a PC when I considered all factors. The last time I traded up for my iMac Pro I had not spent a single dollar on the maintenance of the previous Mac Pro, I got more than 60% of the purchase price of the Mac Pro when I sold it, and I never lost a single day's production to machine or software problems. The Mac Pro was not quite as fast as the Alienware machine I had in the office for most of the same time, The Alienware machine cost about $300 more than my Mac Pro, cost me hundreds of dollars in maintenance, and when I sold it I only got about 15% of what I paid for it. That specific windows machine was the most problematic and expensive system I ever owned when I considered everything. When it was working, it worked just a little faster than my Mac Pro but that small increase in productivity wasn't worth the money. I haven't had a Windows machine running AE for the last 6 years. I think they are a lot more dependable now and have fewer driver problems than they used to but I see a lot more questions from users with windows machines that are having system problems than I do on the Mac side. Until I am ready to upgrade again in about 2 years, I'm sticking with the Mac because of their warranty, service, and reliability until it's time to buy another system. If you honestly compare machines for memory, processing power, and storage a Mac with a really good warranty and service to back it up is going to cost you very nearly as much as a PC from a major manufacturer that has the same specifications and a similar warranty. There are a few professional production houses and professional editors and effects artists that I respect that have switched from the Mac to the PC, and I know that their switch was based a lot more on analyzing the true cost of owning and maintaining their machines than OS preferences because that's how you stay in business.
So here's my question to you. What kind of projects are you planning on working on? What is your budget range? How comfortable are you troubleshooting driver and system problems? Have you considered the total cost of owning and maintaining your hardware and software? Did you budget enough for archival backup and raid storage to protect your work product? Is video production a hobby or a profession? No matter what you plan to do, start with the Adobe After Effects system requirements on PC & Mac (2020 ...
Meet all those minimums for any system you purchase. Unless you are a hobbyist with a lot of free time and some extra cash, purchase a system from a major manufacturer that has a good warranty and a place you can take the machine for repairs. Fix it yourself home-built systems are almost always more expensive in the long run.
Whatever you do save a couple of hundred dollars for some external drives so you can back things up, make a bootable clone of your system (boot drive), and keep it current so you can revert to a working system when an update kills your system in a few minutes instead of a few days, and you'll be fine.