If you dont know either One Piece or Dragon Ball then you better go google or local comic bookstore to have a look! The Top of the Best sellers. Got 3 in the list as I know. One Piece, Dragon Ball and Slam Dunk. Each of them sold 100 millions or 1 billion copies world wide… I am not sure on the figures but they are good!
http://bbs.fxdm.net/showthread.php?t=131655
Check the link above. Recently the author of One Piece and Dragon Ball has cooperated together for a short comic 😀
Have a look! It worth your time if you wanted to see Gouko (悟空) from Dragon Ball again!