The more i think about it, the more it seems to me that the one about Letho is probably the only one that has a noticeable impact on your options..
Or maybe there's more but I didn't notice it.
Anyway, I would suggest:
- You traveled with Iorveth (doesn't affect your interactions with Roche much, and who knows if it could significantly affect your interactions with Iorveth when they'll add it)
- you spared Adrian
- you spared Sìle
- You spared Letho
- you spared every-fucking-one (no, seriously, I can't remember what was the fifth).
Or maybe there's more but I didn't notice it.
Anyway, I would suggest:
- You traveled with Iorveth (doesn't affect your interactions with Roche much, and who knows if it could significantly affect your interactions with Iorveth when they'll add it)
- you spared Adrian
- you spared Sìle
- You spared Letho
- you spared every-fucking-one (no, seriously, I can't remember what was the fifth).
The rule of thumb - if you killed someone, they won't be in TW3. So go with sparing everyone to get more quests and character interactions, if you are interested in this kind of thing.
Well 1)Adrian just unlocks some lines of dialogue.
2)Sheila a short sequence plus very minor choice
3) Letho gives you a quest in place of another one (a witcher contract) so I guess yes for storyline value?
5)I think it's the romance option? The rose?
I think if you spare Aryan, Louise goes with you and Voorhies, so you can talk to her as well. Otherwise she is pissed, stays in Novigrad, and you go only with Voorhies.
Well, I'd say spare everyone. Some of them can help you while the story develops, such as Letho later on, but sparing people is a good deed anyway, though you could look up the names and find out what happened and decide for yourself, I have played the previous witcher games, 1 and 2, I have read the books, yet I just spared everyone because I wanted to meet them all once again 
^_^
^_^The only choice that matters is Letho, and I think we'd all agree you want him alive.
Here´s a list of the choices and consequences from TW2 - http://forums.cdprojektred.com/thre...consequences-(SPOILERS)?p=1695680#post1695680
But to keep it short, sadly nothing really matters that much. Except for Letho.
But to keep it short, sadly nothing really matters that much. Except for Letho.