Weeeeell, the sad part about Loghain (which I never recruited on my two complete playthroughs), is that he's one of those "Last moment"-companions. I can't say much more than that as I've never experienced playing with him but that's one of the reasons why I never got him... you get him "too late", but it's also depending on how the Player wants to experience their story.I dunno if this is canon or mod but there's a similar thing with Sarevok in Baldur's Gate... people talking about how they recruited him. Is this a mod or canon? Regardless, "Last moment"-companions is something I hope Obsidian avoids.
I actually pick him up most of the time- unless I'm playing a City Elf (in which case the incident right before the Landsmeet is a dealbreaker), he comes across as a well intentioned extremist who does everything to protect Ferelden from Orleis thanks to his paranoia. Despite coming in late, he has some great dialogue and really won me over after my first time using him. Alistair, on the other hand, seemed mostly petty in the end- while I do agree with him being upset, you really do need a great general like Loghain, so there's no reason not to put off his punishment until after the Blight (especially considering the twist, which Riordan really should have mentioned sooner).
But yeah, would have loved to get him sooner!
As for Sarevok, he actually isn't hidden at all- you get him right at the start of Throne of Bhaal and it can't be avoided short of flat out telling him to go away after he offers to join. You get him for the full expansion- less time than anyone else, but he has plenty of impact on the story, including a full redemption track to make him Lawful Good.
Edit: Or was it Chaotic Good? Been a long time since I used him, not sure. It was the same law/chaos value as his starting alignment though.