What's the best one?

 

I've been mostly on ED visas. I had to switch to a 90 day single entry TV which I got from HCMC. because of timing issues I may need to get another tourist visa after this one. My guess is Yangon or Savannakhet would be a little better than Vientiane but curious what the forum thinks.

Vientiane is absolutely fine (even best) if you can get an appointment. You cannot apply there otherwise. 

 

Savannakhet is OK if you apply on a Tuesday or Wednesday (assuming they are not preceded or followed by public holidays). They can be unbelievably busy when visa run companies bring groups. Travel is a bit of a hassle.

 

Last I heard, Yangon is pretty good, but you need to arrange a Myanmar visa. Also, you will be returning to Thailand by air, which might conceivably be an issue if you are an extreme long stay tourist.

 

In my opinion, you are asking about the three leading contenders.