Perhaps, though as noted above giving her enough Humanity seems to end that for her.
You can save Solaire without killing her, you know.
Of that list, Gaping Dragon. Even Pin-dick and his clones can land a stray fireball once in a while.
Same as Matsczon, my vote is Petrus, no contest. I'm not as big a fan of Patches as most, but he at least has a lot of personality as well as being a useful merchant who's easy to get back to Firelink, and while Lautrec is a murderous zealot he's a big help against the Bell Gargoyles* and, no matter when or where you kill him, has some sweet loot (including a nifty suit of armour). Petrus is just a skeevy fat a-hole whose presence the game essentially makes you tolerate (up to a certain point) for no reason.
*(Yes, I know he can be summoned against the Gaping Dragon, but that's no big deal to fight solo so...yeah.)