There has always been a number of questions regarding which Thai embassies expats normally use in and around Asia. These are the embassies which most expats and foreigners use in Thailand with a note of their Thai visa process times and what they normally will and will not issue being a bit about the embassy procedures. Note that this was correct at the time of writing and that timelines and procedures do change over time.
Thai Embassy in Laos
This embassy is very strict with regards to issuing tourist visas. They normally will only issue a single or a double entry tourist visa for the year. Once you have had at least 2 tourist visas in your passport they will not normally issue you with another. With regards to a business visa. They do issue a business visa but only if you have the correct documents from your school or business. This is where most companies in Thailand send their prospective employers too. Note that the visa is issued overnight. Note that when you enter Laos you need to pay a visa fee for your Laos visa. This will vary on which country you are from.
Thai Embassy in Penang
This Thai embassy is very strict with their business visas. Once you have had 2 business visas and have no applied for a work permit they could very well place a red stamp into your passport not to return to the embassy again. Visa abuse in Thailand is a major issue and the government has become very strict about this issue. They will also normally only issue 2 tourist visas per year before they advise you to obtain the correct visa. A marriage visa in not a major issue but again they will normally only do 2 back-to-back visas before they advise you to extend the visa in Thailand for 12 months. The visa is also issued overnight and there is no visa fee when you enter Malaysia.
Thai Embassy in Cambodia
The embassy in Cambodia has become extremely strict with regards to issuing a Thai visa. They will normally only issue you a marriage visa twice back-to-back before they deny you the visa. Also if you are applying for a business visa you need to have all the documents with you from your school or business. Note that if you have had a business visa before at least 2-3 times and had not applied for a work permit then they will not normally issue you another business visa even if you have the correct paperwork. Many expats and foreigners have abused the visa process over the years and since 2009 the Thai government has clamped down heavily on the problem. Note that when you enter Cambodia you need to pay the Cambodian visa fee. The Thai visa process at this embassy normally takes about 3 days and is not an overnight process at the time of writing.
These are the 3 Thai embassies which most expats use in Thailand. If you have any questions then speak to us online or send us an email concerning your visa application be it in Asia or in your home country. Note that each time an ambassador changes normally the process and rules at the respective embassy will change. Also note that none of these embassies will issue a multiple entry business visa, marriage visa or tourist visa. If this is what you are looking for then it is best to apply for it in your home country before you come to Thailand.