Scheme 0 bumping: Thing recently commented on go to the top.
Pro: You can tell where the discussion is Con: encourages Trolls
Scheme 1 Voting: Ala Reddit.
Pro: Democratic popular stuff rises to the top. Con: popular stuff tends to be dumb and scheme privileges majority views.
Scheme 2: following like on some site like hubski.
Pros: You only hear what you like.
Cons: You only hear what you like.
applying combinatorics
scheme 0-1
Voting Bumping
score = (number of upvotes) - (number of downvotes) + number of comments
of course each variable is weighted for time.
order posts by score high to low.
hypothetical pros: Vigorously debated/discussed stay at the top longer even if controversial.
hypothetical con: Weak against trolls but not as weak as scheme 0.
scheme 0-2
bumping and following.
Hard to figure because the two systems are functionally very different but the formula.
rank = time since last comment / (number of comments by people I follow 1)
order low to high.
Scheme 1-2
voting and following
rank = up-votes by people I follow - down-votes by people I follow
Scheme 0-1-2
rank = time / (up-votes by people I follow - down-votes by people I follow + comments by people I follow + 1)
Of course a tradition of community is really the best way.