It's pretty difficult to talk about in the abstract, especially for a homegrown CRM. The best choice may depend on if you have any existing integrations to middleware providers. I'...
John's advice here is good. The first question you'll want to ask when coming up with the definition is really "Will I need to update individual instances of this record type?" If ...
We recommend that all new development be done in REST. REST is the current focus of API development, and SOAP is unlikely to receive any enhancements moving forward.