What do you want in a coil? Are you thinking bigger or smaller?
If you tell us what you're after, and where you'll be hunting (conditions), we might be able to make a few suggestions.
Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
Since I don't know what your using now, I can only guess. If you don't have a small sniper coil you should get one to get between the trash and get only one item under the coil at a time. You can get nearer metal fences and sidewalks that have rebar.
Hard to beat the Coiltek WOT for fields.
For trash there are a number of good smaller coil options. Detech, SunRay, Coiltec.....
Solid bottom coils are best if there is a lot in the way of sticks or stubble where you're hunting.
I use the Minelab FBS800 for my small coil.
Seems plenty small to me.
Found this ring pretty near a Soccer post, found my Kitty Kat pin also with it near a tire ride.
For my field detecting if the ground isn't recently harrowed I use the 15" W.O.T.
Here is the coil with some recent finds:
Recently purchases the NEL tornado for my etrac and I've pulled a few silvers with it. U can see it in some of my vids at youtube.com/diggin1145s tons of silver coin and ring finds