If you already have the health insurance, I dont see why you shouldnt go with O-A. Easy to get the first time. You dont have to worry about visa/going to immigration office for 2 years roughly. Financial requirement is showing a bank statement with 800k baht. It does not have to stay there for months. It does not have to be a Thai bank. Note that this is how it works the first time you get the visa - after 2 years you can choose again what is best for you.