Well, if you want it to be nightmarish, forget ranged options.
I think using ranged magic + priest spells might make it easy.
It depends ! When you only make a pure ranger or pure Priest ... then it's not easyer like other builds (I believe).
But indeed, using a bow makes things more easy in some way ... thinking about how strong Explosive Arrows are, or Splitting Arrows ... Way of the Ranger ...
On the other hand :
as long as you've big fun playing on nightmare mode with your favorite build, that's most important !!
(for me)
I play as a Priest and use a bow mostly for :
1) shoot a arrow to track the attention of a enemy or group of enemies ...
2) using Stun Arrows or Poison Arrows to Stun or lower the speed of some enemies (because I'm a slow player and wish to have more time to react).
And if I find a yewellery item with a skill on I like I use it ! Recently I found such item with +2 to Splitting Arrows (handy to speed up the damage using it close by an enemy!)
I use a 2-handed sword mostly for :
1) to use Thousand Strikes (speed up MY attacks a bit
)
2) to use Rush Attack (superbly after a Stunning Arrow) so I'm very fast close by to give Blind, Charm or Fear a go
3) to protect my Summon Ghost and directly attack those who attack my Ghost !
Furter on I always use Priest skills in battle : Charm, Blind, Fear, etc ...
All this thing together makes the battles more relaxed, fun & entertaining ...
But still, their are moments enough that are thrilling enough to give me the fantastic feeling I'm playing on the highest difficulty !
In fact (in some way) I play a pure Priest because I only put skillpoints in Priest Skills, except Stun Arrows and some non combat skills :
all the other skills (like Rush Attack, Thousand Strikes, Polymorph, Splittign Arrows, ...) I use are coming from skill boosts on yewellery and so on ...
The Death is lurking everywhere 
