The main difference between a ED and a DTV visa is one allows you to open a bank account while the other does not. To me having a Thai bank account is so much more convenient living in Thailand long term. Since you are approaching 50 years old, you may want to explore non-O visas. Paying for health insurance coverage could be cheaper than enrolling in those soft power DTV courses for non-OA visas. It all depends on what you mean by "the near future" and how much money you have.