No ideal graft site for ACL reconstruction exists; they all have advantages and disadvantages. Patella tendon grafts are still considered the historical "gold standard" for knee stability by surgeons, however they suffer a slightly higher complication rate, including knee pain such as when doing a lunge.
Hamstring grafts historically had problems with fixation slippage and stretching out over time. Modern fixation methods of hamstrings avoid graft slippage, producing outcomes that are the same in terms of knee stability with easier rehabilitation, less anterior knee pain and less joint stiffness.
An allograft is a graft from a corpse, usually either a patellar tendon, hamstring tendon, and occasionally an achilles tendon. The advantage of an allograft is the patient does not sustain additional injury through removing a tendon, thus making it faster to recover. The disadvantage is the risk of infection by using foreign bodily materials and the graft is known to be slightly weaker. 
A lesser known, but newer type of graft is a synthetic graft. Little data exists on its strength or reliability, but patients should be aware that the option exists. Typically, age and lifestyle choices help decide the type of graft to be used for ACL reconstruction. The overall factors in knee stability are correct graft placement by the surgeon and treatment of other menisco-ligament injuries in the knee, rather than choice of graft.