Better all around system, Mac or PC?

they are both more or less at par.

For a very carefully configured, very stable system such as a Mac Pro 12 core you will need to have a lot of knowledge and patience on the PC side, or pay just as much of more to Dell or some other workstation seller for an equivalent system. Just throwing off the shelf parts together might yield crappy results unless you really, really know what you are doing, and might not save you as much as you think.

Generally Macs do crash less, as they have a few known configs and software makers like Black Magic can really test and tweak something very specific whereas on the PC side they are aiming fo ran unknown configuration target, unless you buy their suggested PC model which is EXPENSIVE. They also crash less because they are carefully put together and tested - sure they come out with few models, but they take their time to make those models work very well.

Macs also hold their value surprisingly well for resale. PCs basically have no resale value at all within a very short time.

That said on the PC side if you want to SPEND you can get a 16 core system from Dell. On Mac you'll have to wait a few months.