What are the easiest Thai embassies in Southeast Asia for converting a dependent visa to an M visa?

Take a look of the website of the consulate you like to visit. See if this visa is in their program or contact them to get the requirements. As we know requirements for the same visa differs at consulates it is hard to tell which is best, they are all perfect if you meet their requirements.

Reading back, I see your hubby is a journalist. So I'm guessing he has done the online application via the MFA website an been approved.

When I did this 3 years ago, I had to go to the MFA collect the documents and take them to immigration at Chang Watthana to get the stamp. It was, at that time, something that could only be done only in Country and at the BKK immigration office.

Things often change here especially when the media is concerned. But, the MFA will provide the exact and current instructions for him when he receives his approval notification.

M as in married or M media (journalists)?