Where is the best place to apply for a 60-day tourist visa for Thailand, Ho Chi Minh or Kuala Lumpur?

Takes about 5 business days to approve IF you upload your documents correctly and they don't have to email you for additional information. So if you're still going to be in Vietnam for a week (and are in an area served by the HCMC thai consulate) apply online, upload your documentation, pay online and wait for the email approval that will have the PDF file which you print (because it is your visa) and present that along with your passport when you stamp in to thailand Otherwise when you're in Malaysia, do it thru K/L. They have a slower processing time as a rule.. BUT it's just a tourist visa so you should get reasonable turn around time

They will probably ask for confirmation of where you are submitting from

I applied whilst in KL for a 60 day tourist visa it took about 7 working days but that's because they wanted extra documents.