I used to have the W-520U and it was the best watch I've ever owned ...also the only watch/thing I ever lost in my life, I left it at the gym class in school and the next day boom, gone.
My favorite series since 10-20+ years ago is the ProTrek, which I guess it's part of G-Shock but I don't see them in the site. (I guess the PRT-1GPJ is there at 1999).