The better approach depends on how many rows of data from the debatched flat file you are expecting to insert into a DB table. Is it in the hundreds? Thousands? Millions?
If you have a fairly small set of records and don’t expect it to grow or vary widely over time, I would recommend using WCF SQL Adapter to insert the rows into the DB table.
If you have a large set of records (i.e. think ETL, datawarehouse style), you should look into implementing a custom .NET helper class (that can invoke the BCP program from the command line, bulk copying your records in an efficient and fast way to your DB table) that can be called from BizTalk.