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We present a statistical analysis of the tradeoffs between detector jitter and light detection efficiency for TOF PET gamma-ray detectors based on SPAD arrays and crystal scintillators. Results show that increasing the light detection probability is more important to improving the coincidence timing resolution than decreasing the detector jitter for modern scintillators. For a SPAD TDC array with a fill factor around 15% and a detector jitter of 120 ps, it is shown that a SiPM with a 30% fill factor and a jitter of 240 ps will produce a better timing resolution when using a LYSO crystal. Results also imply that SPAD TDC arrays might be competitive in TOF PET with SiPMs if faster scintillators are developed in the future and SPAD TDC arrays maintain a much lower jitter than SiPMs.