You have to understand your requirement and what advantages and disadvantages each of these methods offer and decide what is best for your requirement.
When you have standard objects to load data into the system, then doing it through LSMW is the best option. LSMW relieves you of the pains of mapping, file activities etc. But its disadvantage is that if you have some complex requirement, then coding that into the mapping at the appropriate locations can be very tricky.
Direct input has the advantage of saving time because it hits the database directly without going through screens which will take up the time of loading screens, going through screen flow etc. Disadvantage is that if there are errors, it is very difficult to recover.
BAPIs are real time, so you get the messages back and you have to decide what to do with those messages. So you have to code for handling the messages. Advantage is that you can it is real time so you can do something else based on the return status.
IDOC are asynchronously posted to the application(exceptions are there). Data in IDOC format is persistantly stored and so you don't have to go back to the source to get the data. Disadvantage, apart from being asynchronous, is that formatting your source data into an IDOC can be tedious. Again this depends on whether it is outbound or inbound.
All said and done, LSMW uses all the above methods(Direct Input, BDC, BAPI, IDOC), so you need to make the same decisions even if you are using LSMW. Some BAPIs use IDOCs internally.
You also have to remember that all these data transfer tools came in at different points of time. As SAP evolved, new tools are introduced. That does not mean that newer tools are best suited than older ones, but you have to weigh each one of them against your requirements.
Questions to ask.
Will standard ones achieve all the data transfer or do I need to do a second pass?
Once data is read, do I want system to hold the data in some format or discard it?
Do I need data to be loaded, all or none mode or whatever that can be loaded mode?
Do I have to do additional processing after each transaction(realtime vs asynchronous/batch processing)?
Happy decision making!!!
Srinivas
