I compared both in the air tests and (more importantly) during a real, few hours, hunt where I dug some junk, clad and silver. To get a handle and real comparison, I used both on every target. I tried one and than the other without disturbing the ground (other than disturbing while pinpointing) between the tries.
Here is my take:
Weight and size
are so similar that I don't see any advantage of one over the other.
Advantage: None.
Build quality:
I would not use either to drive nails but they work fine to find some.
Advantage: None
LED lamp. Garretts is next to useless. Minelab's is strong enough to actually help to see what's in the hole.
Advantage: Minelab.
Sound: Garrett has a lower pitch and appears to be louder but this could be due to my partial hearing loss - I can't hear high tones as well as I used to. To my wife Minelab sounds louder but, she is younger than I am and she can hear high tones very well. Still, I can hear Minelab well enough to call it a draw yet, some of you may prefer Garrett.
Minelab sound can be turned off so there is only vibration feedback. To do this with Garrett, one would have to disassemble it and cut some wires.... My recent fav. spot is on the church grounds (have permission) right next to a cemetery... Sometimes in parks I hunt right next to people with babies in the strollers. Guess what?! I give a definitive
Advantage: Minelab.
Vibration:
Garrett has strong vibration you can't miss. Minelab's vibration is more gentle. Kind of like Garrett would be yelling: ""It's here stupid!" while Minelab would gently pat you on the shoulder saying "Excuse me sir, I don't really want to disturb you but what you are looking for might be right here..." I didn't have problems feeling Minelab's vibrations even through the thick gloves yet I wished it was stronger. so:
Advantage: Garrett.
Sensitivity:
Minelab sensitivity can be set from high to low. In air and real life tests, I found that Minelab's high is virtually the same as Garrett's normal sensitivity so,
Advantage: None.
Sensitivity, de-tuning - working at very close range:
Garrett can be de-tuned by turning it off and than back on close to the target. Minelab can be de-tuned the same way or by pushing on the "-" button.
Advantage: Minelab.
Sensitivity, supertuning - extending the range by placing a coin (or other metal) in the proximity of the On / Off button, close to the rod portion of the pinpointer so the pinpointer almost goes off.
The technique works equally well for both models.
Interference: While pinpointing, I learned to put the detector behind me and never had issues with either one so, this reminds...
Advantage: untested - not an issue for me.
Conclusion:
Either one of these pinpointers do very well what they were designed to do. Personally, if I was to be left with only one, I pick Minelab mainly because the sound can be turned off at will.
YMMV
HTH