If you are an avid hunter with a Prizm or Coinmaster series detector there are a few different coils: 8" round, 9" spider, 950 round, and the 4 x 6" DD style "shooter coil".
Each one will have it's own pluses and minuses.
First the 8" round. It's excellent in brush and vine type ground cover as it doesn't have any open holes to catch on things. It's fairly easy to pinpoint with too. The smaller coil size lets you hunt in trashier settings with less target masking.
The 9" spider is lightweight and you can easily swing it for hours. It's very easy to pinpoint with as it it has a hole in the center which lets you see exactly where the 'middle' of the signal is. However, you may find it challenging in brushy areas as it can get tangled up. As the coil sizes go up you'll go deeper but face more masking with other nearby targets.
The 950 gives you the most coverage for open fields and areas where you don't have a lot of trash. Pinpointing is very easy with the open hole in the middle and it'll go deep, but you may find it more difficult in trashy areas as there is less target separation.
The last coil is my favorite: The 4x6" Shooter. This coil is very small so you won't cover much area but the DD coil gives a pattern in the ground that is sharp and well defined. This is THE coil for detecting trash filled areas, next to concrete sidewalks, and around concrete borders for playgrounds. It also is excellent at detecting along fences and close to metal poles, playground equipment, and other places that most coils won't go. Pinpointing takes some getting used to. Check sided to side for the best signal then front/back for the best. Once the target is centered under the coil go back toward you with the coil and when the signal drops off the target is off the front of the coil. Dig there.
If you haven't tried these different coils check your dealer to see if they have 'em in stock where you can give 'em a try. You may find yourself hooked on a different coil. My Prizm IV has been fitted with the 4x6 Shooter coil and I haven't taken it off since.
Hope that helps!