Dang, really wish I'd seen this thread before I submitted mine, I had to be very, very general in some ways, and I said my character should use a magic implement which it turns out is, ehh, not the case for their class. Hopefully I can make some strategic edits after Feedback...
Just for my 2 cents, I think everyone should think not just about themselves, but also in context, as a player, when designing their items and NPCs. Sure, it might be great to see everyone wielding your Smoking Brand of Icy Destruction Katana-Axe when they charge the Big Bad Evil Guy, but helping people get to that point is just as noble a deed and nearly as memorable. Case in point, who here played Fallout: New Vegas? Who's first character was a Stealth/Guns type? Now, which do you remember more fondly, the Anti-Materiel Rifle you used to clear the game with, or *Ratslayer*? Sure, it wasn't a great anti-Deathclaw weapon, but that gun (for the uninitiated, it was a low-tier Varmint Rifle with all the upgrades, scope, magazine, silencer, plus reduced weight) could easily carry you all the way to Vegas and back out again, letting you massacre low-level threats like ghouls, NCR patrols, etc. with utter impunity. I never, ever sold Ratslayer in any playthtough, it's the sort of weapon you retire on a wall mount before you ever think of parting with it.
So that's my challenge to at least some of you. Mercy is a heck of a find, and everyone likes their Thermic Lance, but Ratslayer is epic without being epically powered. I think it's better to be wielded or worn for the entirety of the game's first half than to only be donned for the final couple of hours. EDIT - For self-spoilers.