Although most bike places rent the conch cruiser with pedal brakes, Tropicar on Duval and Key West Bike Rentals ( http://www.bikerentalskeywest.com/) both have bikes with hand brakes and gears.  The island is flat so you really do not need gears but hand brakes are easier and more comfortable as there are multiple stop lights and signs and you can stop more precisely using hand brakes.  Key West Bike Rentals delivers bikes to your hotel and seems to have better quality bikes than Tropicar.  Tropicar has only a small inventory of geared bikes with hand brakes so you should reserve them in advance.