Regular outlet vs bootleg ground vs ungrounded GFCI vs grounded GFCI
A properly grounded 3-prong outlet protects against these types of faults:


short to neutral or ground should trip the breaker.
open neutral will not cause a hazard.
a heavy load will raise neutral voltage (due to wire resistance) but ground will remain at 0V.
in addition, electronics will be properly grounded and surge protectors will work properly.


A bootleg ground will protect against a short but


open neutral may put full line voltage on the ground (through the device plugged in) producing a lethal threat.
a heavy load will raise ground above 0V, causing a hazard.


A grounded GFCI will provide the characteristics of a grounded standard outlet plus


current flow between hot and any ground (presumably through a person) will trip the GFCI and prevent electrocution.


An ungrounded GFCI simply removes the grounding for electronics: some sensative devices could malfunction and surge protectors will not work correctly.