I would like to see the threads ordered in chronologically newest reply. It should be bold. If I read it then it should be unbolded. Then afterwards, if it gets a new reply to be bolded again.
This is how Latest works now with the exception of going bold again—that only if you actually scrolled the whole thread... If there are still any unread posts in the thread when it gets a new reply, it would not go bold again ... which seems correct given you didn't have enough interest to read the whole thread in the first place 
Having said that, I'm also thinking about adding an option to keep bold always and instead just show a zero count that is slightly faded when the post is caught up AND show unread post count even on never-opened topics. I guess some people have trouble reading the faded version.
It also might be nice to see the avatar of the most recent reply rather than thread creator. Obviously that changes if yet another reply happens before I refresh. Simply that when refreshed the avatar of the last reply shows.
Let me think about that. I started out that way but found it confusing. It would be nice to show both OP and most recent respondents avatar...