My personal favorite night of HHN is the final night. The entire "atoms-fear" is completely different from other nights. The scare zone actors are more energetic and so as the maze actors. Everybody is having a good time plus there are a few HHN traditions that they do on the final night. The downside of going this night is that it is relatively crowded. Last year I was able to complete all of the "E Ticket" mazes before the night was over. I'm sure you could too. Also patience of waiting until the last night would be killer!
A lot of people say to go on a Thursday since it is rarely to crowded. I totally agree with that if you aren't very busy the following day (you will be very tired).
Stay away from opening weekend! It is always really crowded! Going after Halloween should guarantee you AT LEAST 3 mazes.
Going to HHN and completing all mazes in one night without FOTL is really about strategy. The crowds flock to different mazes first every year. There is no way of knowing until a few nights in.
LAST YEARS STRATEGY:
Skip scaremony all together and head to Halloween and Exorcist 1st. Go on which of the two has the longer wait. Then head to The Backlot. Once you complete everything you want, EAT at the food truck. Rest up. Go to the upper lot and enjoy some terror tram. Afterwards hang out in the scare zones (take in the "atoms-fear"). Second to last do TCM. Lastly, chainsaw chase out.