Low weight: tubulars obviously. It is not possible to build clinchers (tubeless or otherwise) that are lighter or stronger than tubulars using the same materials and designing for the same wheel strength. Look at the tubular rim profile: it is perfect; no fragile or heavy 'hooks' or protrusions required to hold the tire on. Smooth edges that avoid pinch flats.
You are going to save 100 grams per wheel with tubulars, again, all things being equal. Plus you won't get pinch flats, you can run your tires at pretty much any pressure, and you won't crush the fragile rim hooks when you run over something. But the biggest advantage to tubulars is that when you suddenly flat, tubulars are a hell of a lot less scary. I've had many blowouts on both, and the tubular blowouts have been calm and controlled, whereas the clincher blowouts have all been terrifying, and tested decades of bike handling skills, sometimes not successfully.
If you want sealant, then you can inject sealant in tubulars. Remove the valve cores and inject 20cc. There: as much flat resistance as tubeless.