The age old question of Attack speed vs Armor pen...
I actually think it's pretty easy to choose to be honest
Nevermore: Higher attack speed slower arrow travel speed no energy reductions 15^50 useless poison modifier
Darksteel: Slower attack speed Higher arrow travel speed 20/20 armor pen 15^-5 energy no useless poison mod pretty skin
so a lot of people prefer the Darksteel because it's a more complete bow, with no ugly mods you'll never use. However i consider the -5e a huge detriment to the overall balance of the class, especially when running with the 10e cost ignite arrows generally when i hunt (with Nevermore) i'll fire off my first shot, use my Preparation or Troll unguent, and by the time they're done casting, the charr are halfway to me so i can fire them down.
there's so many more pro's and cons you can delve into, but in the end it's the preference of the user.
I don't have a ranger in pre, and I don't have the bonus weapons, but I do know this:
flatbow > longbow easily, slower arrow speed is not gonna hurt you against mobs, because most of them barely even move and they don't attempt to dodge on purpose. Flatbow has way higher DPS than longbow.
In addition, sundering mods are pretty weak. Also considering the low armor/hp/level charr have, a sundering trigger might not even speed up killing a charr at all if it doesn't lower the actual number of shots required to kill. Either way, I am pretty sure the sundering mod is going to be negligible compared to flatbow dps anyway.