If you paln to stay longterm, the best would be a 'Non-Immigrant' visa with 'Multiple-entry'.
It is valid for 12 months. With this visa type you will need to exit and enter Thailand at least every 90 days to get a new entry stamp allowing you to stay a further 90 days.
You will propably NOT get a Multiple entry visa in neighboring countries, your best chance of getting it is in your home country before you arrive in Thailand.
Thai consulates in US, Europe and Australia seem to be the most generous.
