If you need the best performance possible performance in After Effects, this workstation with an Intel Core i7 9700K or Core i9 9900K is currently the best you can get. There are certainly more expensive CPU options available, but the latest versions of Ae are not able to take advantage of higher CPU core counts which makes the relatively affordable "consumer" Intel CPUs the current king of performance.
However, one thing to be aware of is that this platform limits the amount of RAM or system memory you can use. It is still capable of up to 64GB of RAM (which should be enough for most After Effects users), but if you have especially large and complex projects, you may want to consider our "High RAM Capacity" workstation which is capable of up to 128GB of RAM. That system will be slightly slower for rendering each individual frame, but is capable of holding twice the number of frames in RAM Preview.
If you are not sure which hardware choice is right for you we recommend reading through the Recommended Hardware section. And as always, don't hesitate to contact one of our sales consultants if you require assistance or a hardware configuration that is not covered by our recommended systems.