Which processor is best for After Effects? AMD or Intel? Why?

Looking at two popular benchmark sites, Pugetsystems.com reports show AMD look best, while aebenchmarks.com shows Intel at the top.  It's very hard to measure accurately, as every configuration is different.

I wouldn't get too tied up in the CPU wars, just follow the golden rules:

After Effects needs CPU speed above all else, rather than extra cores.  Buy the fastest CPU clockspeed you can afford.

If you use a lot of GPU accelerated plugins, like Element 3D, or you work with Cinema 4D etc, spend extra on a good GPU.

After Effects needs lots of RAM to work well.  These days 32GB is a bare minimum, I'd be looking at 64GB on any machine I bought, at the very least.

I highly recommend the expertise at pugetsystems.com. I bought my custom computer from them. They really know their stuff. They develop all kinds of benchmarks, and test all kinds of hardware, and make results public. If you choose, they can also build you a fantastic machine based on their research, what work you want to do, and what software you want to use... and unnecessary upselling is not a part of their business model. No, I don't work for them. Just a satisfied customer. I can't answer your question but I know they can.