I'd say Hack is harder than Nethack. What matters is how much of the game you know. In Hack, if you have bad luck you are basically screwed; in Nethack, prayer can get you out of lots of trouble, you just have to know it's there to rely upon and not to use it too often.\
Nethack also has many ways you can use resources, even bad resources, to survive. Take bad or useless potions and dip them in water to dilute them into plain water, get them blessed to make them all into holy water, then use that to bless your other items to get much more use out of them. Wash scrolls to make them into scrolls of blank paper, then use a magic marker to write the scrolls you want on them. Combine these two tricks to make blessed scrolls of identify and find out what many, if not all, of your items are. Drop extra rings down sinks for clues as to what they are. Use wands to write on the ground for clues to their identities.
This is a different play philosophy from Hack, where in large part you take what the game gives you and do the best you can with it.