Smaller Coils are much better for Target seperation....the Larger Coils are good for large "Clean" Areas....if you are in a junky place..Small coil...if you are walking around for 5 minutes every signal..then the Large coil is good..
its all about where and what you are hunting. I used to have the ACE 250 small coil...and a year or so after, got the bigger coil