Personally, I am a fan of large coils. In the places I hunt, depth is everything. We have very moist, non mineralized soil in my part of Iowa do the coins sink deep. Also there is not much trash to deal with in the places I hunt, like old small town parks, churches, homes, and schools. My preferred coil and detector combination right now is a Minelab Etrac with a NEL Hunter 12.5 x 8.5 inch coil. I can get the deep coins and navigate through the little bit of trash. Occasionally, I find a site that is trashier than the Etrac can’t handle, and that’s where I bring in my Nokta Makro Simplex with a 9.5 x 5 inch coil mounted, which is the smallest one I own at the moment. The first detector I had 4 years ago was a Garrett Ace 200 with a 6.5 x 9 concentric coil mounted. I just find that in my areas, depth is more important than separation. I do plan on getting a 6 x 8 inch SEF coil for my Etrac though.