I picked others. There are tons of good mangas which aren't included in the first post.
These are the top 5 mangas according to one manga. I've read them all. Review time!
Naruto - Easy to understand drawings, page turning addicting nature. Although, it has a slow moving plot.
Bleach - Hard to understand manga, the anime is much better in my opinion. I don't rate the manga very high.
One Piece - Everything is very longwinded in this, and I find myself wanting to skip chapters. A lot of the characters aren't very good design wise either. I don't rate the manga very highly for this one either.
Fairy Tail - The only one in this list which hasn't been made into a anime yet(its coming out in the fall of 2009), it is also one of the best. Although the story so far doesn't really have a big plot to it(it hasn't got nearly as many chapters as the others in the top 5), it's enjoyable and fun to read. It also has a humour to it which the other four don't have.
Historys Strongest Disciple Kenichi - It doesn't have any plot, but while reading it you aren't really bothered. I find myself cheering when Kenichi wins a fight and staring at the girls in the skin tight clothing. If it had a good storyline, this manga would win.
Winner for me is Fairy Tail. I would read it.