Giving me a demographics is a bit wrong thing to do, since I read almost everything there is.
Well, I started out with Naruto back in 2000 as my first manga. At that time I was more centred towards Shounen in Anime form (I.E: Inu Yasha, Naruto, Kenshin, Mahoromatic ++). As I started to get more interested in manga and anime, I went over in the sports world and started to explore it. To my amusement I liked it, so I wanted to go futher into it and I found Omanga/Hawks where I got blessed with the Seinen (Jirashin, Berserk, Leviathan and not to forget Living Game)
But I think it was around 2003/2004 I first started to jump into shoujo world with manga like Perfect Girl Evolution, Gong, X and etc. The humor got me off guard and I liked how they mixed goofy humor with art in some of the series, while other series like X where they really made some amazing characther developement. So I decided to jump little bit into Josei world, since Shoujo gave me more laughs then I had anticipated - So I went through some of the manga from the great people over at Condensation and I liked it. Sure, it was smutty at some point, but I liked it nevertheless.
So my lesson in all this, I think all demographics has something in offer in some form. I just about finding what you like and how you like it to be presentated - I am very art orientated and I'm driven my either story developement or combination of seeing the people in manga really strive to achieve their goals.
With that said, I can't really pick any of the demographics as the best or the worst. That's like choosing between my favorite meals, the only thing that changes is my mood and what I want that day.