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).
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?
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 ^_^