Most metal detectors today , Whites, Garrett, Fisher, Minelab, Tesoro will give you pretty good depth in their mid to upper priced detectors. Most will come with 8" 9.5", 10", and even 11" loops. Some have better target separation then others, many have audio target I.D. and can sound like a machine gun going off if you get enough targets under the loop or in some cases depending on your discrimination settings can completely blank out over all those targets,and it will drive you crazy trying to separate all those targets to decide which one to dig.
I used to own a Fisher CZ-6 that had a 8" concentric loop and had great target separation and depth which made it pretty good to use in fairly trashy conditions, but even it had it's limits if the trash become heavy enough.
Unfortunately the parks, schools,and public properties we hunt today are pretty well littered with trash, and though occasionally you will pick a good coin out of areas that arn't to trashy most of whats left to get good targets out of are in those trashy areas.
My present machine came with a 11" coil and it has pretty good target separation and see through abilities , but even so I found it necessary to purchase a smaller coils to work through that heavy trash. and I have been very pleased with what it can do. Yes I loss a little depth but my finds are far more then making up for that. So no matter which brand you buy give some consideration to a smaller loop to work that trash. You won't be sorry.

Rick