probably best to get it for your main, best or most used system. personally i grabbed gog.com version. it's like steam, but with no drm which should future proof it better than steam.
that and a physical copy. i hope they won't start sending physical copies just yet, i want it to be a feature complete, bug free, standalone copy, not a potentially buggy mess with half of the stretch goals missing, requiring day one patch. unless i misunderstood that part and all the stretch goals are already finished too.