From Forum Nokia Wiki

Before selecting the SDK to be used for a particular project you have to consider which features are needed and which phones support them. Then, once the targeted devices set is established one can opt for either using one binary compatible SDK (so that one application build will work on all devices) or build the application with each SDK flavour, in order to add SDK specific features to specific application variants.

The image below shows the list of S60 SDKs and their device coverage.

Please note that while there is no binary compatibility break between S60 3rd Edition and S60 5th Edition it is very likely that you will have to reconsider your UI design as the touch features introduced by S60 5th Edition cannot be fully exploited by a legacy build.

Note: The S60 3nd Edition MR SDK is commonly used for maximum compatibility.

Related articles

S60 SDKs and Plug-ins compatibility