One piece? Two? More? The surface texture is important, too. Too crinkly and they are hard to clean. Not crinkly enough and they are slippery. Thickness, especially in "high traffic" spots is a consideration. Time to install, take out for cleaning, etc. would rank high on the list. Maybe even reversable might be cool if it's possible.
If you're shopping for fabricators, see if it's possible to have some anti-fungal or anti-mildew chemicals added to the mix. Sometimes a wee bit of moisture trapped under certain kinds of rubber and rubber-like compounds will start growing "stuff" really quickly. One of my friends is the guy who "invented" TEVA sandals back in the 80's when we worked together as Colorado River guides. One of his (and everybody's) biggest problems with them early on was that the rubber he used started to stink to high heaven after "xyz" immersions in river water and coatings with beach sand. Man, you could smell an early TEVA a long way off. We used to spend a lot of time scrubbing them to knock back the smell. It was a pain. Eventually he figured out a way to solve that problem. It's something to think about, especially for the "mudder" crowd and others who use their Zukis in wet situations. We have a really pesky leak in our 87 and we have to air out the carpets after each rain greater than .25 inches. What a pain.
Anyway, it's something you'd want to consider before production. Thanks for asking for input and Good Luck!