durable, versatile - Single Speed
fast- Fixed

pretty much the only difference is u can "coast" on a Single gear (the bike will move when u dont move the pedals)

Single Speeds tend to have thicker tires, and Frames.. so u can ride on bumps/ holes/ just generally rough terain. I live next to a board walk, and a Fixed Gear tire can get stuck in there

Fixed come with Track tires, super thing,

if you will only ride on Roads get a fixed, if u want a bike u can beat up a little w/o worrying about the wheels going out on you Single Speed