Best iMac or MacBook Pro for Logic Pro recording studio upgrade

I've been using Logic for more than a decade and it's time to upgrade my system. My current iMac is a Retina 5K, 27-inch, Late 2015 with Retina 5K, 27-inch, Late 2015 3.3 GHz Quad-Core Intel Core i5 with 16 GB RAM and is obsolete. I want to jump back into the fray with new gear. I have adequate hardware with instruments, mics, amps etc in my studio but I'm about to upgrade the heart with a new iMac or MBPro and I'm trying to decide which. It will be mainly in-house use (as opposed to portable/live recording) so which computer should I get as the core of a good/better/best rig?

[Re-Titled by Moderator]