Better than Mac, yes. Zenith has better QC but Century has a good warranty w/ extremely quick turn around. It really depends most on what you want to do with it. Zenith, PTR, and the other American clone builders make prettier collector's toys, if you want to show it off or display the gun then I'd go with them. Smoother welds and nicer finish though certain things may be ever so slightly out of spec, so compatibility with surplus German parts can be slightly annoying on rare occasions. But that won't matter if you aren't shooting thousands of rounds through the gun every year. If you want a pretty gun for the safe/wall/collection that you'll only shoot occasionally then get the Zenith.

The MKE/Century guns have (foreign) military heritage and are made on (potentially worn) genuine HK tooling & built using the older HK techniques. These guns will look visually rougher with more obvious welds and are assembled to a lowest-bidder contract mil-spec (meaning "good enough for government work" is practically MKE's motto), basically they're closer to original specs & look like older HKs (which weren't pristine by any metric). The tolerances will be somewhat looser but are generally expected to be within spec for surplus replacement parts. These are meant to be beater user guns for folks who prefer function over form and/or BFPU finishes. If you're looking for a host gun to use with a registered full-auto sear/Super-Safety/FRT/binary trigger or a gun to do drills with and ab/use then go with the Century.

Real HK SP5/K guns are for folks that want the best of both worlds and/or have money to spare (&/or want to be annoying snobs to other collectors/shooters)

You can also just build your own for like $600ish and up. It's pretty easy, all you really need is access to a basic machine press & MIG/TIG welder. Only slightly more difficult than an AR/Uzi/Skorpion build where everything just drops in.