I have been confused about this, so I am posting a chart and explanation. Hope it helps
-Query is designed to best search/manipulate features ON THE FEATURELAYER you have already added to the map. [with the .selectFeatures() method ] Also it is best for spatial Queries on the server.
-Query is not designed for searching accross multiple layers. (it would take a loop and huge SQL expression). No dynacmicLayerInfos, no LayerDefinitions, LayerIds, LayerOption.
----------------------------------
-Identify is designed to manipulate features ON THE MAP, so it has lots of DOM properties like dpi, width, height, etc..
---------------------------------------
-Find is designed to search ON THE SERVER accross multiple fields of multiple Layers without having to create your own loop or SQL expressions. Find is limited as it can NOT do spatial filtering.
[ATTACH=CONFIG]13498[/ATTACH]
