We talked about this, it depends on too many factors. If you mentioned what type of hunting you were doing, what type of sites you were hunting and what type of ground ( mineralized or not mineralized) you were hunting that would help narrow the choice.
The 12" will get deeper but would most likely be worthless in any kind of trash. The 6x10 would be better in trash but isn't as deep as the 9.5" unless the ground is mineralized. The 9.5 gives the accurate depth readings and is deeper than the 6x10 in good ground but is a little big in trashy areas.
here's some stuff I've posted before;
Going to larger coils simply increases masking in many cases, and only in clean sites can you get that extra inch or two.
With the stock coil, the audio respond is deeper than you can get an accurate visual VDI. As the coil size increases, the VDI quality decreases, and often a smaller coil improves VDI quality.
Concentric loops like the 5.3 have the following advantages:
Can get good targets under bad targets because of their cone shaped field
They are 10% quieter regarding magnetic interference from power lines
They have 10% better trash discrimination on iron - steel bottle caps and foil
They can shape the target without walking around it
They pin point accurately
Wide Scan Loops (DD) like the 6x10 have the following advantages:
They have better side by side target separation
They are more sensitive to smaller than coin size targets
They are more sensitive off the tip area of the coil
They smooth out the ground reactivity noise by 10%.
So no one coil can do it all. With that said there are many people who would vote for the 6X10. Rob