Sometimes I know the lead of the story before I start, sometimes I have to think about which boy would fit better with the storyline, which one would give more dynamic to the story. Chronos Project was almost a Nick centric story but Kevin fit too, depending on how the story went. If Nick had been the lead, the story would have been likely different. Severed Identities couldn't be any one other than Brian, I had briefly flitted with the idea of using Kevin but knew with what happens that it would impact Brian more, he would have a harder time with the events. I started a story for the Howie challenge that after starting realized it would be better as a Nick romance, though it's on the back burner.
I've never thought after a story was finished that another boy would have been better in the lead of the story because the story forms itself around the boy that I did use as the lead. If I had decided to use Kevin for the lead in Severed Identities it would likely have a completely different feel but it would be a story where you wouldn't be able to see anyone else in that role other than Kevin, just like I feel now you can't see anyone else other than Brian in the story as it is.
I've deleted ONE story from AC. More Than That: All or Nothing... I wasn't happy with where it was going, I didn't plan on working on it ever again and didn't really feel like anyone would miss it so I deleted it. I don't think I'd delete any of them now unless I made them original fics for publishing.