The first time I played through and got the Ebony Blade I just decided to go around Skyrim and gather every Hireling and just kill them at Gjukar's Monument (I think that's how you spell it) but then when I was done and Ebony Blade had finally reached it's full power the world just felt more empty and tampered :/ I want to leave all (or most) Hirelings alive this time around. I now know that if you do a favor for someone you can kill them and it counts towards the upgrade for Ebony Blade. Does anyone know of any pointless people who I can do a quest for (then kill)?

It may take awhile but kill your spouse the blade and mephala really like that. It may take a few times but you can cut down the spouses you don't like that way it won't matter as much.

WHOM CAN I KILL?!

Anyway, now that my grammar nazi is satisfied, it depends on whom your friends are, which depends on which radiant quest or favors you have done.

http://www.uesp.net/wiki/Category:Skyrim-Quests-Miscellaneous-Favors

This might help

From UESP:

Although any NPC with a relationship value of 1, 2, or 4 will power up the blade when slain with it, some are more suitable than others. To minimize the repercussions of enhancing the blade, it is often beneficial to choose targets with replaceable functions, such as the owners of mills and mines, or those who must be slain during particular quests.

...Not 3?

Yeah, whenever I have to kill someone (lets say for DB in Oblivion), but don't want to get arrested, {I kill the daedric followers, because no one cares about them
I

Kill Faendal he's useless, use the Ritual Stone to revive him, kill him again then wait 24 hours and use the Ritual Stone to bring him back and kill him again as many times as you need to. Btw if you decapitate him the ritual stone won't work.

Jaree-Ra and Deeja count towards the blades kill count. I think the Argonian who'll enter Ironbind Barrow with you counts.

slightly off topic, but does anyone know how the ebony blade currently works with regard to one-handed vs two handed perks/skill level?

got this from the uesp
"The Ebony Blade is wielded in two hands, but is considered a one-handed sword rather than a greatsword. This means that it gets the benefits of a generic two-handed weapon, such as using and training the Two-handed skill, but also benefits from abilities that apply explicitly to one-handed swords, such as perk and enchantment damage boosts, power attack and decapitation maneuvers through the one-handed perk tree, and bonus critical chances^?. Its damage, weight, weapon reach, sound files, impact force, and stamina usage are all configured to One-handed skill values. Because of this odd amalgamation of benefits, the Ebony Blade struggles to find a niche. It appears to be entirely dependent upon the Two-handed skill, One-handed perks, and One-handed enchantments to increase base damage (e.g., fortifying Two-handed does not increase its base damage). Since it raises Two-handed, it can be beneficial for late-game One-handed players raising stats for levels. Although helpful in early levels of Two-handed, in higher levels this weapon will level the skill very slowly. This may be due the fact that it receives its stat boost from One-handed but its Two-handed damage is still the base level of 11, or the fact that the drain effect does the bulk of the damage for the weapon."