Generally I prefer Arabic numbers or hatch marks. Ironically, if Romans are done well I love them. I chose the Roman version of my least "affordable" watch, because I loved the abstract simplification that happened when Nomos used a sans-serif single width font. There is probably an exception to every rule.
Roman numerals are very much a no-go for me. If someone GAVE me a watch with them, I'd wear it out of politeness, but I'd never buy one. Well, never is a strong word... let's just say at this point in my life, I don't see me buying one.