Imac is still a good choice if your main work on after effects only fully spec. imac is a great choice but if you also do video editing and any plan to upgrade in future then you have to go with windows i recently purchased a dell’s workstation for very heavy video editing work and also assembled a workstation for after effects with these specs.
Main reason to go with windows is you can add nvidia’s powerful GPU that you can’t add in imac or on any mac and AMD is not a good GPU at all.
After effects system:-
Processor :-
8th Generation Intel® Core™ i7-8700K 6-Core Processor (12M Cache, up to 4.7 GHz)
Ram :-
64GB, 2666MHz, DDR4 16×4
Storage :-
1. 256GB M.2 Samsung 960Pro PCIe x4 SSD (For OS)
2. 1TB M.2 Samsung 960Pro PCIe x4 SSD (For Running Projects & Cache Memory)
Graphic Card :-
NVIDIA® GeForce® GTX 1080ti Founders Edition with 11GB GDDR5 Graphics Memory
Data Drive :-
2×6 TB Seagate Ironwolf Pro in RAID 0 (For Data)