Mr0TYuH: I have to disagree, at least concerning Roche's path. If you save Triss, you slaughter the Nilfgaardian delegation and prevent them from completing their plot. Triss implicates Sile in the kingslayings, and there is some violence against mages. Overall, however, the Conclave is formed; most mages are unharmed, and diplomatic relations between the northern kingdoms are normalized. Roche is declared an outlaw, but he does rescue Anais, although Dethmold escapes, and takes her into hiding. The Nordlings are united diplomatically; the rights of mages are recognized, and the northern kingdoms are in a better position to face the Nilfgaardian invasion.
If you chose to save Anais, the Nilfgaardians, using Letho, implicate the entire Lodge of Sorceresses. A massacre of all mages, not just those belonging to the Lodge, begins. Only a few of the most powerful escape; the vast majority are killed. The Conclave is not reinstated. There are no formal relations between the northern kingdoms. Anais is either handed over to Natalis, who in deeply in debt to Philippa, or Radovid, who probably had her brother killed and probably would kill her if it benefits him. Either way, she is probably safer on the run with Roche. The North is divided, and most of their mages are dead. With the Nilfgaardian invasion starting, it does not look good for the North.
As far as the Roche path goes, I think saving Triss is by far the better choice. It is a more difficult decision on Iorveth's path, though.
Thank you for the clear reply. I see the Nilfgardian die both in Iorveth and Roche path, and even the outcome is pretty much the same (with the differences about Roche and Dethmold).