Yep, for both KO and Sub, I've typically done a combination of fastest/most interesting along with highest resulting rating for the fight. And I'm not one to necessarily stick to giving it to one of the top 3 or 4 fights on the Main Card. If a fight early on the card warrants it with those conditions, I absolutely give it.
For FotN, I typically go with highest rated fight if it wasn't due to a one-sided affair with a quick KO or submission. I'm not into giving both fighters an award for FotN if one gets steamrolled. But a high rated fight that lasts a little longer, has a finish, or even goes to a split will definitely get my attention. In this case, if it's a title fight or one of the top two or three fights on the card, yeah, I'll give that a bit more consideration and weight if it's close with an earlier fight, but I have no issue giving FotN out to an earlier fight either if I feel it warrants it from a rating/results perspective, especially if I feel that the fighters in that early fight really went out there and fluffed the crowd up for the later fights!
Different owners use different criteria. Common ones I've heard/seen are fastest KO (not tko), fastest (or rarest) submission, and fight of the night can go highest rating on a longer fight, or a big rivalry important fight...a few ways.