I'm a bit of a noob to Esri still so I have a few questions regarding these two types:
What is the difference between DynamicMapServiceLayers and TiledMapServiceLayers? Do separate services need to be published to use each type for a single map? Are both valid types one can use in Esri's FLEX API?
Best Answer
A dynamic layer generates an image each time the map view changes - panning and zooming, turning sublayers on/off, etc. This image is then served in your map viewer.
A tiled layer is pre-cached on the server, as a series of small images optimised for each zoom level - as you change the zoom level, a different set of image tiles displays. This allows the server to display the information very quickly (as with the background tiles on Google Maps).
Typically a dataset would be more suited for one format over another (eg a geology layer is probably quite complex and doesn't change very often, therefore it would be suitable for caching) but there's no reason why you couldn't also serve this as a dynamic layer.
You should create a separate non-cached service in this case.
Yep, you can use either type. Note that there is also the option to stream vectors directly to the client as feature layers.