For parks and tot lots, I'd go for the 5.75 inch concentric. I'd also go that way working around homes or where there are or were buildings.
The first accessory coil I got was the 12 x 10 to cover more ground at the tot lots, then it started to teach me about real world hunting and masking. I went back to the standard coil and then bought the 5.75 inch. The 12 x 10 does not get nearly as much use as the other coils for most of my hunting.
The 12 x 10 is what you want to consider for open areas like woods, plowed fields or open areas with not a lot of targets or trash.
I like the clean sweep for sports fields and some tot lots that I know are pretty clean where I just want to cover area and not necessarily go as deep. It doesn't lose too much depth, but it does lose some when compared to the standard coil. Does not mask quite as much as the 12 x 10. Total area under the coil for the cleansweep is about 65 square inches and the 12 x 10 is about 95 square inches; but being 18 inches long, the cleansweep covers more ground area per sweep.
With the Cibola, coil to coil performance also depends some on how well matched the particular coil is to the particular detector. (Think slight variation within the manufacturing tolerances.) With ground balance things can be adjusted, but with the ground balance of the Cibola an internal setting, changing coils could give you exactly what you expect, or things could be off.
With the Cibola and the coils I got, things went well. It was set up pretty well for where I normally hunt.
Cheers,
tvr
