I only tried SR3 and uninstalled it after three hours in disgust: the game is clearly designed by and for douchebags, white nerds trying to sound "gangsta". I'm much too old now for this retarded shit.
Saints Row 2 is REALLY good. It actually manages to play multiple conflicting moods with the 3 storylines (you can tackle the 3 enemy gangs in any order).
The Ronin (Japanese biker gang employed by a megacorp) is a mostly serious story where close friends die or get horribly injured and the villains are sympathetic. It still has some good jokes in the quiet moments, including my favorite gag in the game, but is pretty dark overall.
The Brotherhood (Overly muscled tatooed punks with modifed trucks) is a mix with the main character driven by revenge, but with the execution is some pretty nice black comedy.
The Sons of Samedi (drugy college kids) is mostly comedy, but actually pulled off well. Missions include destroying drug farms by helicopter mounted machine gun and being stuffed into a hotbox limo and having to kill a bunch of guards while stoned.
You should try it (you will need mods to fix the terrible porting though)