As stated, MKI won't physically fit in the A3000 so it is not even an option. Also if I recall correctly, the MKIII almost always has problems with soldering of the cpu socket going bad which is not an easy fix for an amateur, and can be expensive for a pro to do. That brings us back to the MKII. There might be good reasons why it is the most used accelerator by the Amiga.org community.