Hello,
There is no such benchmark on performance for document posting. You can use any of three BAPI, Batch input or IDOC. May be in BAPI there are few more structures . All has got different applications. Like IDOC is for exchange data between two 2 sap system. BAPI can be used to execute sap from non sap system. Another like in LSMW you can import file . Consider the error processing. If you have error during processing who is going to correct? You or business? You have to think which is best for business.
So, what is best for your option that is important not BAPI, BDC, IDOC or LSMW,
Thanks & Regards,
Abhijit