I'm a fan (and you should be too) because...I like the band for who they are and what they make.
I know how difficult it can be to write good music, and these guys totally pulled it off. The lyrics in their songs are originally and catchy. The rythem in their songs is unbelievable. I have loved Boys Like Girls since 2005, and way before they have gotten big. Even though they are big and famous now, I support Boys Like Girls just as much as I did before they recieved all this fame.
I'm a fan that won't go screaming in their faces about how much I love them because there are other ways to tell your favorite band how much you love them. Just drop a thanks for coming to my town, or saying thanks for something that they gave you, that's all it takes, and it shows them that you care about who they are as people. You don't have to be obnoxious at their shows either. Usually, when I go to their show, or a show in the same music genre, I only jump around for a little while, because I think jumping around and acting like an idiot defeats the point of being at the show. I go to shows to see my favorite bands jump around and sing my favorite songs, so usually I end up just standing their bobbing my head in time with the drums, with my hand moving in sync. And obviously, I stare up at the stage in awe.
Okay, so now you all now why I'm a fan, and how I act as a fan.
Is this a contest, or just something fun? lol because i had a lot of fun writing it.
Do John, Bryan, Martin, and Paul read this? thatd be sweet if they did.

oh, and having a favorite in the band is okay, but make sure that you recognize all the guys in the band. That way, when they think back to when they met you, they all will remember you as the person who acknowledged the whole band, and didn't spend all your time with one of them.
But do what you want, thats just a word of advice from yours truly.