Should I buy a tourist visa or use visa exemption for Thailand as a US citizen returning to convert to a non-B visa?

The user is considering returning to Thailand as a tourist for the third time in six months after previously holding a COVID visa extension converted from a non-B visa. They are contemplating whether to purchase a tourist visa or rely on visa exemption upon arrival, while also wondering if it's advisable to have 20,000 baht and proof of onward travel. A comment suggests that obtaining a tourist visa could be safer due to potential entry issues.