I use plenty of premium dictionaries, if one's budget is, Copper: Dictionary - WordWeb Audio Dictionary > Advanced English & Thesaurus, Silver: Dictionary - M-W Premium > Dictionary.com Premium > Chambers Dictionary > Dictionary Pro, Gold: Erudite Dictionary & Thesaurus > Oxford American Dictionary & Thesaurus > New Oxford American Dictionary > American Heritage English Free, Diamond: Oxford Dict of English & Thes. > ABBYY Lingvo Dictionaries >Collins English and Thesaurus > Webster's Dictionary+Thesaurus
My primary dictionary is on Touch English Dictionary - Premium rest of them are used for reference. (There're certain areas where these premium dictionaries failed to address like: pop-up, back-up etc; on a whole it suites my needs.)
Those who're interested in purchasing dictionaries from MobiSystems make sure to use it for the entire trial period (30 days) & then proceed to cart. It is worth mentioning, I requested them for a few changes they're kind enough to incorporate it like look up words from other apps etc. Thanks to MobiSystems.
P.S: Webster's Dictionary+Thesaurus (MobiSystems) has got nothing to do with Dictionary - M-W Premium (Merriam-Webster Inc.)
Coming to ABBYY Lingvo Dictionaries I purchased 'English Explanatory Set', so is the resultant screenshot.
ABBYY Lingvo Dictionaries
Courtesy: Various dictionaries' screenshots