As you had already mentioned that extended services are natively integrated with HANA, so it’s going to be easier to use against HANA but as it is native to HANA only it can’t be used elsewhere. It will be faster when you compare it against ODBC because the extra step will be avoided here as it is native to HANA. Also, as it is integrated other factors like latency and other would be out of question which can be considerable factors with ODBC.
Extended Services follow the MVC architecture so you need not worry about the implementation style as it will take care by itself. ODBC on the other hand is more like server technology where you need to take care of architecture. It depends on your future scope as well if you require lot of custom things to do; ODBC with API is the solution to go with otherwise XS will solve most of your use cases.