Is it better to apply for a retirement visa in the US or Thailand?

The O visa you have to have the 800,000 BHT 2 months before and 3 Months after. The other months you can go to minimum 400,000 BHT

I have a friend that has used both the one you get from outside of the Thailand and the one you get inside Thailand. He tells me there are different insurance requirements.

If you plan to live in Thailand for a long time then might be worthwhile to come on Tourist Visa, open a Thai bank account, fund that with 800,000 baht, convert to a Non-O visa in Thailand at the Thai Immigration office for about 2,000 baht. Toward the end of the 90-day permission to stay from that visa apply for a retirement extension showing 800,000 baht seasoned in a bank for at least 2 months. From that extension, costing 1,900 baht you will receive permission to stay for one year, which can be reapplied for in subsequent years. You are then required to keep at least an 800,000 baht balance in the account for two additional months and for the remainder of the year the minimum balance of 400,000 must be maintained.

The reason to do it the above way is that you free yourself from an obligation to have general health insurance from a Thai insurance company that has been approved by Thai Immigration. If you come on a Non-OA you will be obligated to fulfill this requirement each year you get a retirement extension based on this original Non-OA.

The advantage of a Non-OA is that you can avoid having to tie up money in a Thai bank account for at least a year or possibly two. But to get that extra year of permission to stay you would need to leave and re-enter Thailand which might require quarantine (as it currently does). Also, to continue with the Non-OA in the future you would need to leave Thailand and return to the US to obtain your next Non-OA visa. In pre-covid times leaving and entering countries was much less problematic. The disadvantage of a Non-OA is that you are tied to the health insurance requirement and there's no way to escape it other than what I outlined in the first paragraph.

Yes 800.000 baht

if I do OA in the U.S. do I need to show a Thai bank?

I’m doing it in USA for sure!

Its very straightforward to get the OA in the US and then you dont have to deal with immigration for a year except the 90 day reporting.