If you want to do target shooting, get the target sight. If you want to do action shooting like IDPA and IPSC, go with fiber optic, but replace the front sight too. You can have a fiber optic front sight and a target rear sight, but not the other way around.
A target sight is better for the precise sight picture you need to shoot bullseye. A fiber optic front sight allows you to acquire your sight picture faster for action pistol sports. A fiber optic rear sight without the fiber optic front sight would just be a distraction. IMHO