MF is potentially more precise, especially if u have the luxury of time to mount the camera on a tripod, switch to LV and magnify the area u're focusing on.
this is particularly useful when shooting macro where DOF is very shallow.
but AF is more convenient, esp if its just a casual outing with family / friends where precision is not that crucial. with a 50mm prime on a 1.5x crop body, shooting at F2, DOF is quite ok with your friends 5m - 8m away from you.
with a kit lens, shooting at smaller aperture, DOF is even more generous. its even harder to miss