What's your use case?
The iMac has its limits, but it's also a decent value (when you factor in the screen). I've had two -- a 2013 and now a 2019. I also tried out the base and upgraded models of the Mac Mini prior to settling on my '19 iMac. I had a very specific use case (audio production) and the iMac "just worked" a lot better with my equipment. I went with the base model because it was 30% off and, surprisingly, it's very capable for my needs--but I use thunderbolt NVME storage for high I/O tasks. I can also boot the OS from NVME as well, although I do that much less often than I expected as the fusion is fast for startups and opening my regular applications.
Based on rumors, we're probably 6 months out from a new iMac Pro and I would guess that 2021 will see a redesigned iMac. So long as you won't get the "itch" to upgrade over the next 18 months, I would scoop up an open box or refurb i5 3.7 ghz with (minimum) 2tb Fusion Drive. They are currently $1700-$1800 open box at Best Buy, if you're willing to do an inspection. Micro Center has some decent deals, too.