The current top comment. IIRC it was fluctuating wildly while it was on the front page. After it's gone, comments can get reshuffled, because some people might keep replying/reading/up&downvoting (arguably those with more of a "vested interest" - likely those that disagree with the original article)
>>Solace+X
Also, does it suggest that the most engaged HN readers (who come early to topic discussions) have a starkly different opinion to late comers?
>>tomp+(OP)
The ordering is also not just by score. Newer comments get some time at the top as well and then decay to what I assume is their scored position.