What is the best visa option for an American married to a Thai citizen and living in Thailand?

okay, you're too young to get a retirement visa so that's off the table.

That means it comes down to a marriage visa/extension or raising half thai child visa/extension.

As people said the easiest and most trouble free VISA would be to go to the thai consulate in either Savannakhet Lao or HCMC Vietnam and get a year-long, multi-entry Non-Immigrant Type O visa based on marriage to a thai. Those consulates do NOT require proof of funds so you could get it with minimal documentation. Now that visa is valid for a year, and when you enter you get stamped in for 90 days, when that runs out you go to the border, stamp out of thailand, stamp in and out of another country then back into thailand to get a new 90 day stamp. You can get 15 months of stay (in 90 day increments) out of that year long visa.

Hands down that is the most trouble free way to go.

If your married and have the marriage certificate with the rose border you can get a non o based on marriage 0bt in a thai bank in your name only seasoned for 2 months.

Or you can go to savenerket loas or HCMC VIETNAM

And get one with out showing funds.

Retirement is 0bt seasoned for 3 months and you can't let the funds go below 0bt

Worst advice is getting visa exempt entries and tourist visa, slightly more better is getting ED visa's to bridge 2 years. As you mention you have a Thai wife and a half Thai daughter, you can apply for the Non Immigrant O visa or based on being married to a Thai National or based on having a half Thai child.

You can stay long term based on being married to a Thai. You can wait two years and come using an O-A visa. Look at the Thai Consulate websites for the several requirements for an O-A visa. Search this group for the requirements for stay based on being married to a Thai.

Long term stays for people under 50 years of age are difficult. I guess I would add that you shouldn’t abuse tourist and education visas.