What part? Fat Boy, Fat Bob or Street Bob?

Would be nice if someone could show briefly where the significant difference is with these models. I would like to add another cruiser. I already had a Yamaha XV 1600 Wild Star Silverado, BMW R 1200 C Montauk and BMR R 1200 CL. I tend to the Fat Boy. Why does the Fat Bob cost about 3 bills less? I don’t understand the Street Bob. When is this recommended? As said would be nice.