You must use transactions if your Web services are to conduct business of any significant value.
Your choice of which transaction technology to adopt should be based on your own internal needs, and the technologies used by your business partners. It is not sensible to adopt BTP if your business partners have adopted WS-Transaction.
Transactions (like security) are one of those things that appear simple to implement and deploy, and whose development effort is usually grossly underestimated. Give serious consideration to buying or outsourcing transaction processing that you require, unless you have sufficient manpower and specialized knowledge of the area.