Laptops are bad choice if you plan to use parallel port, but you speak about UCCNC, Ethernet and USB, so it is not a problem. I am using both Laptops and a desktop, none of them are bran new, the weakest is the laptop which is HP Probook 6470b. It handles UCCNC and UC300ETH without any problems, so if you want to be sure of good functionality and reliable operation then get the UC300ETH or the UC400. USB should be avoided if you have an option, but performance wise USB should also work just fine.

In fact, I don't think UCCNC is a resource hog at all, so I am pretty sure you can run it reliably on almost any PC which it can be installed on. Maybe even on an XP, but definitely W7 or W10 machines.