What is the best visa option for an American married to a Thai citizen visiting Thailand for 3-4 months?

Non o is cheaper than metv but metv would be easier if looking 4 months

As an American you won't get visa on arrival, but a visa exemption for 60 and maybe in december only 30 days. This can be once extended by another 30 days at local immigration.

Easy ,if they drop.the 60 days to 30 days arrive visa exempt ,then get the vist thai family visa for 60.days .and if need be do a border run for another 30 days .

Or ...metv

If your marriage was registered in Thailand then you can get the extension easy. If you were married in the United States and did not get your Marriage Certificate authenticated here in the US and by the embassy in your area. Then, that takes quite a process. If you need help with any of that I completed that process, it took me about two months. I was married in the United States and had to get my married certificate. Authenticated.

Is your marriage registered in Thailand?

If it is, that makes you eligible to apply a 60 day extension of stay based on visiting family.

Combine that with either the Non-O for a total of 150 days, or a regular tourist visa / exemption ( if still 60 days ) for a total of 120 days.

As you're married to a Thai get the Non-O to give you 90 days on entry with the 60 day Visit Thai Family Extension giving you a total up to 150 days

Get a 90 day Non Imm O visa based on marriage

Are you talking about the DTV? That's the only visa that gives 180 days. But you can't just get it because you want it. You have to qualify for it.