Twitter seems to value the individual, but devalue the content. (E.g. low quality posts by a famous person)
The former is more meritorious, inasmuch as the vote base can accurately judge a comment. The latter is more consistent, in that popular people stay popular (and admittedly, are popular for a reason).
Personally, I prefer the HN-style model, but I also believe it only works as long as the ratio of HN-encultured users to bad / average actors stays above a certain threshold. From a technical and vote system perspective, HN isn't that different than Reddit: what makes it HN is the culture and community.