Viz media's Ikki and Signature line of comics have been proving to be some of the best out there. Well, I should say the current version of this line of manga. My first experience with it was when I found out they decided to release Dogs the Prequel and the manga ( haven't heard of any word for the side ones though). And now they've recently released the second volume of March Story which is best described as the love child of D.Gray-man and D.N.Angel.
Length: 3+ (series is still ongoing)