Personally I feel that Geocaching with Geosphere is the best geocaching app out there.
It can access over 4000 caches and will work with the iPad and iPod Touch. Is supports pocket query downloads, field notes, highliting, multiple sorts, filters and much more. I use the Bad Elf gps for added accuracy.
I have Motion X HD and several other geocaching apps including the one from Groundspeak.
It seems geosphere was less than $9.00.
You can create multiple Groups with geosphere, I even have a group that shows my gold claim marker locations. It allows you to snap a screen photo of the map for off line location viewing.