IMO,
HHN is crowded every night. Sure, it'll be less crowded than a Friday or saturday, but I have never seen a HHN with low crowds. But, you should be able to get everything done.
HOS on the other hand should be perfect on Monday night. The only night HOS every gets huge crowds is a Saturday, and every other night basically features almost walk-ons for all the houses.
Also, in the house department this year, I do believe HOS beats HHN (I finally got a chance to experience all the houses at HOS.) And yes, before anybody calls me out, I do work at HOS, but this would be my honest opinion even if I didn't.
You can't go wrong with either event, and you shouldn't have a problem no matter which one you choose.