23fbaf81_ess___Photographically_Curious__Mirrorless
[Overall] Auto focus [SLR] Very quick in single and continuous mode. For optimal results the AF system must be well-aligned and calibrated (individually for each lens). Only advanced bodies allow AF calibration by the user. AF is quite slow in live-view mode unless phase-detect sensors are built directly into the sensor. The first body outfitted with such sensors debuted in 2013. [Mirrorless] 
Can be very quick and precise in single AF mode. No alignment or calibration is needed as the focus is read directly off the imaging sensor. Continuous AF and subject tracking are quite poor unless phase-detect sensors are built directly into the sensor. Several cameras with such sensors debuted in 2013.
SLR vs. Mirrorless | Photographically Curious
Mirrorless