Have to agree with Andre. RFC fits a lot of people's comfort zone and they immediately gravitate towards that option.
But it is outdated and quite awkward to work with. It's very much an inside-out development process (fitting your resource model to BAPI that is not a resource model) , whereas I find the outside-in approach much more efficient (build a resource model abstract with a resource based implementation).
Learn to use the Service Builder, once you get to grips with it, development of services is much faster.