here you go, my take on it ...
I kept him alive.. blood thicker than water and all that.
glad i did.
you might want to kill Roman (you sick b'stad) but im very hapy with my choices.
lets face it.. kill your cousin and you got kate, no Roman to finish your days off in Liberty city with yeh? no one to go drinking with, bowling.. what about the taxis?
then we have the little matter of other girlfriends from the dating site.
so you let kill off your cousin for the girl, only to cheat on her to get your 100% with the other girlies!?! ...i shake my head in woe 
i let Kate die, i dont regret it.. I read last night what happens when Roman dies.. its not nice.
so thats what i did!
its great that this game gives you choices! because either you can play like a nice guy or a bastard! and I know for most of my days as Niko, he wasnt nice.. loyal yes, nice no.
it also makes it hard to slate in the press for being a bad game, because not only is it more adult this time around, but the choices they give you make it not such a bad game if you choose to be nice.
you have to hand it to R*, this is one hell of a game!!