If I remember the dialogue correctly, then Iorveth only asks Geralt to accompany him to Aedern- he does not ask directly for help with making Saskia a queen, implying that Geralt could have a choice in the matter.
Iorveth makes it clear that he's going to aid Saskia (assuming that you ask him all possible questions when you get the chance) so it's obvious that choosing Iorveth's path means that Geralt will get caught up in Saskia's rebellion.
The way the game sets it up, Roche's path comes across like Geralt helping his friends (Roche saved Geralt's life, and the Hangover quest was a real bonding moment between Geralt and the other Blue Stripes members), while Iorveth's path is more along the lines of Geralt being an idealist who wants to work towards equality (Iorveth hasn't been at all friendly in Act 1, and the Scoia'tael have actively tried to kill Geralt for most of the Act, so main reason to join them would be due to wanting to learn more about Saskia or else because Zoltan asked it).
We know in hindsight, that Roche's path takes longer to leave Flotsam, but there's no way Geralt could have known that for certain.
I think both paths take roughly the same amount of time to leave Flotsam (depending on play style I guess). And based purely on what Geralt knew at the time, he has no reason to think that killing Loredo would take longer than freeing a prison barge.
And since he had no way of predicting that the mist would appear, not to mention the dialogue saying Triss didn't have precise coordinates, I don't think it would factor into the decision whether he starts off at Henselt's camp or Vergen. They're only a few minutes' walking distance from each other (or at least they would be if not for the mist).
That's why I think Geralt would make the decision mainly based upon who he felt he could trust to help him, and by that point in the game the Blue Stripes definitely seemed more trustworthy and eager to help since they wanted to find Letho as well.
This is assuming that Geralt told the Stripes about his treachery. Actually, how could he have when he don't see the incriminating letter till after his mansion is raided? Please correct me if I am wrong, I may not be remembering correctly.
You can listen to the mission briefings for both missions before you decide whether to choose Roche or Iorveth. In Roche's mission briefing, his main reason for killing Loredo is that Loredo has made a deal with Kaedwen and needs to be killed for being a traitor. Roche discovered that on his own regardless of whether Geralt found out independently.
And earlier in the game before this discovery Roche makes a comment about how Loredo won't let anyone leave the port. I'm sure everyone disabled the ballista at Roche's urging, but that can't be the only weapon that Loredo has at his disposal to attack ships. I also vaguely remember some dialogue on Iorveth's path saying that the Blue Stripes ship had been nearly sunk by Loredo even though I destroyed the ballista, but I'm not 100% sure of that.
In any case I still think it made sense to kill Loredo before leaving the port, and the Scoia'tael probably should have done that too before they freed the prison barge.
I think there's a lot of subjectivity in these claims, so let's steer away from this. If you're interested, however, try to evaluate both paths without personal preferences.
The game does a good job putting supporting reasons for both sides, so people are obviously going to feel that a stronger case was made for one side or the other depending on which reasons they think are most important.
Trying to be as objective as possible, I don't think there's any good reason for Geralt to choose Iorveth considering only what he knows in Act 1. However I think in terms of long-term consequences things probably work out better on Iorveth's path freeing Saskia.
I originally intended to import my Iorveth save into TW3, but then I replayed the game on both paths after the Enhanced Edition came out and I realized that I kept thinking of the Roche path as "what actually happened" because it was darker and it seemed more fitting to me, like it's more authentic to the general atmosphere and lore of the Witcher universe.
I have heard the "phillpa's errand boy" term before, and I don't understand why some people get that feeling. He works in conjunction with her, but she's not in charge of his quests.
She is in charge though. On Iorveth's path, Act 2 starts off with Geralt having a few-minute long conversation with her followed by a fuck-ton of quest updates because of all the things she asked him to do
On Roche's path he has to do some investigating and discover on his own how to lift the mist curse (he already knows the general idea but needs to talk to people and find out what the specific symbols of war are). And for lifting the curse on Henselt Geralt is indisputably in charge, explaining to Dethmold what needs to be done and telling Dethmold what to do in order to help.
But on Iorveth's path, he doesn't do any of that. Philippa tells him which two items he needs to lift the mist curse (and finds the other two herself), and for curing Saskia (which is equivalent to lifting the curse from Henselt) she just tells Geralt which items to fetch for her. Geralt doesn't have the same authority or a chance to display his own knowledge and experience.
Geralt simply feels a lot more autonomous on Roche's path, investigating things at his own pace with Dethmold and Henselt looking up to his expertise and respecting his judgment. But Philippa looks down on him as a convenient tool who will do what she says without questioning it. That fits her personality of course, but I prefer to see Geralt in his element where he knows what he's doing and can make his own decisions about how to accomplish his goals.
I am not particularly fond of either Roche or Iorveth, I am only concerned with Geralt's interests, and Triss's safety would count among them. So that's where I am coming from in this whole...thingy. ›››
I understand that
However I don't personally think that either path is more likely to find Triss based on what Geralt knows at the time (and in actuality too). There's no evidence in Act 1 indicating that Letho and Triss split up, so no reason to think that the choice came down to following Letho on one path or Triss on the other.
On my first play-through I figured that Henselt was Letho's target so I assumed that Henselt's camp was where he actually wanted to go. And since I knew Letho and Triss went through the same portal I figured I'd find Triss wherever Letho was. (Although my primary motive was simply that I trusted Roche more and thought he'd be more helpful finding Triss and Letho.) It never occurred to me that Letho would simply let Triss go. I thought he'd keep her prisoner in case he needed her to teleport him away after killing Henselt.