I think the easiest trait for N! depends on your play style. Generally I only take ammochain for Ao100 or for a specific challenge I think it will work well for (AoMC actually), but that has a lot to do how I play. My 'standard' N! build as of late has been Bru->Bru->Ber->TaN->TaN->Bad->MVm->Bru->TaN, but that's because I think melee is fun.
In terms of the most useful N! hints I can give is that I play UV and N! a lot differently. UV I take my time, meticulously clearing the level and searching for power-ups. This works well because of the fact that mobs stay dead, so you have all the time in the world. In N! every in-game moment counts, so I'm much more likely to just grab power-ups as I see them, not when they could give me the most benefit. The less time spent walking around, the less time things can spend raising. Killing a mob twice does no good unless it is dropping ammo that you need. If you find the stairs you need/want to take, really think about if you need to go try to grab another small medpack ~40 steps away, or if you can do without it. To put it in perspective, out of the few times I've done the Mortuary in N!, I don't think I ever bothered finding the Angelic Armor, because it wasn't worth the risk (which makes me wonder why I do the Mortuary in the first place....).
I generally stay out of Hell's Arena in N! unless I've found a combat shotgun and even then I still have to feel good about the medpack /power-up situation. A few factors that play into that are that I generally get TaN and not HR, I use technical mods on weapons over agility and the agility usually go on boots to make up for no HR. My last ammochain character went firing speed instead of accuracy, so it's not much a loss for me not to pass up the free agility mods in the Court regardless of my traits, but again, it's my play style. Although if you want to do the Arena, a combat shotgun is a near must. Shoot in the dark until something hurts, then keep shooting until you can see it. At that point it's up to you which weapon you feel better about. Keep all the corpses near the center, ideally so there is very little walking involved to kill everything, because the faster things die, the less you have to kill. This is the reason I prefer the combat shotgun over the chaingun, shooting one target often hurts 1-3 that you can't see, softening them up before they can see/attack you.
In the end, my rambling comes down to do everything as quick as possible (in-game not real-time, it's not uncommon for me to stop in the middle of combat for 30 seconds or so to really consider my next step or two).
Also few small general tips;
-If you're fighting near water/lava/acid, make the finishing shot in close with a shotgun or rocket launcher if you're taking distance to knock them to water/lava/acid thus disposing the body.
-Abuse berserk packs and invulnerabilities as much as you can, as they give double time in Nightmare.
These are definitely worth stating again, I pretend I'm almost invulnerable when I'm berserk and less corpses is just more better.