I never stopped liking Nick, but I did find myself shaking my head sadly at him fairly often. The Punk'd episode is a perfect example. Oh, Nick... LOL. But remembering how he was then just makes me appreciate the way he is now even more!
I might as well answer the rest of my question now. As I've already said with Nick, he was my least favorite at one point, early on in my fandom, and is now a close second favorite. I write about him a lot more now than I did when I started writing fanfic.
Brian has always been my favorite Backstreet Boy and still is and always will be, but if I'm being totally honest, I probably did love him a little bit more back in the good old days of Frick & Frack and before the Husband/Wylee days. I like Leighanne (most of the time), but sometimes the two of them together are just ridiculous, and I think that's totally her influence. I'd still marry him in a heartbeat, though... and make him stop wearing scarves and carrying manpurses and homeschooling his son.
I used to make Brian the lead in just about every story I wrote, but since he got married and had Baylee, I've been writing about him less and less... it's just hard to ditch the baggage.
AJ used to be my second favorite after Brian, until he was replaced by Nick. I still like him, though, and he's probably my favorite to write as a supporting character in my stories.
My love for Howie and Kevin has grown a lot since probably about the Never Gone era. I never paid much attention to either of them before that, but I've come to appreciate them. Kevin leaving was probably good for my Howie love because it gave Howie an opportunity to step up and show more of his personality, which I quite enjoy, but Kevin coming back has increased my love for Kevin tenfold! I've never liked Kevin more than I do right now. And while I never really wrote about either of them in my stories, other than as supporting characters, I'm giving Kevin a lot of attention in Guilty Roads and have an idea for a Howie novel messing with my head right now. They're both bringing more balance to my writing.