It should be this simple: New entries at the top, and entries with new comments below that (never mind new 'like it' adds). But it also needs some way to show exactly which reason it is in that order so you know how to far down to go to see new content before reaching old content. If multiple entries had new comments since the last time the page was loaded (or the entry viewed? Whichever is the finer grain control that they have) then they should be left in the same order they were first published in (ordering them by the latest comment change is also acceptable, and easier).
LiveJournal could also benefit from a view like this for new journal entries and comments of friends.