Hello Newbe,
I like the stock coil most. It has good depth and good separation.
Right now I have a 7" concentric coil on my Silver, and it works very well.
It is a little more sensitive to small gold jewelry than the stock coil.
I've been using it in tot lots and the 7" works a little better for that.
But, the stock coil will do just as well and even better in most situations.
I find the stock coil works well in trash, but the smaller coil will give a little
better separation.
The 5.75" concentric works really good also. It's hot. I have not tried the 4".
Some people don't like the stock coil, but I have had good results with it.
I am fortunate enough to have a choice of five different coils.
I keep a 5.75 concentric on my Euro Sabre, but occasionally use a 12'X10"
concentric coil
I have a 5.75" concentric coil with my Vaquero, but can use the 9"X8" stock
coil with it for relic/ artifact hunting.
I use the 8" stock coil and 7" mostly on the Silver.
If I only had a stock coil and wanted another one for a Silver, it would be the 4".
HH,